It's the great unanswerable question that has haunted Linfield legend Isaac Andrews and thousands of his club's supporters for 50 years ever since they came within 420 seconds of springing one of European football's most unbelievable shocks against Manchester City.
The Belfast Blues had, against all the odds, been holding the mighty Manchester Sky Blues, with world-famous stars like Francis Lee, Colin Bell and Mike Summerbee in their £1m-plus line-up, to a 0-0 draw at Maine Road in the first round of the European Cup Winners' Cup, but with just seven minutes left on the clock, City scored after Andrews, the rock-solid sweeper at the back, was injured in a clash of heads and had to go off.
The man who broke the deadlock - and Linfield hearts - was Bell, whom Isaac had marked out of the game, and the livewire Shankill Road man, now in his 70s, says: "I always wonder if I hadn't been forced to leave the pitch with a split eye, would we have gone on to get that draw at Maine Road?"
Blues manager Billy Bingham, later to inspire Northern Ireland to World Cup glory in Spain and Mexico, has never been in doubt that an 11-man Linfield would have gone back to Windsor with a clean sheet.
Reports of the match on September 16, 1970 said that Andrews' equally reliable defensive partner Ivan McAllister was blinded by the floodlights at Maine Road and 'lost' the cross that led to the Bell goal, which left Bingham with a cut hand after he punched the dugout in frustration.
"I'm not saying I would have been able to stop the goal but I like to think I would have been there to do something about it," insists Andrews, who's still a regular in the grandstand at Linfield's home games.
Andrews, a survivor of the Blues' seven trophy-winning team of 1961-62, says City manager Joe Mercer spoke to him after the Maine Road game and said the Blues were unlucky to lose, but added that his players had been glad to see the back of him.
Another stalwart of that Linfield side, Eric Bowyer, says Andrews was the undoubted star of the show in Manchester.
"He didn't put a foot wrong. And things could have been very different if he'd still been on the park," insists Bowyer, who went on to manage Linfield and still follows the club.
Bowyer says the 1-0 defeat and the 2-1 win over City at Windsor a fortnight later were the highlights of his European career, though the disappointment of being eliminated on the away goals rule still rankles.
"Nobody gave us a chance," says Bowyer. "City won the competition the year before and their coach Malcolm Allison reckoned his players were on a sure thing.
"But Billy Bingham had other ideas. He'd just come to Windsor as our manager and he had us believing that anything was possible. He also had us fit as fiddles. We trained at least four times a week, and that stood us in good stead for Maine Road."
Several years ago, Bingham told a video that I made and which failed in a search for TV footage of the City games: "I gave them training they'd never had before and they didn't like me too much at the beginning. But eventually they got some great results through the hard training and hard work we put in there."
The Blues flew over to Manchester the night before the match and stayed in the Airport Hotel before heading to the stadium where hundreds of Linfield fans were waiting to greet them.
"It was a sight to behold, and the supporters geed us up for the match during which there must have been 1,500 Linfield fans behind the goals, and they never stopped cheering and singing us on," recalls Bowyer.
"I was told that some of the supporters made their way across the Irish Sea on coal boats."
Personally, I'd been on a more traditional mode of transport, the Liverpool ferry, where Linfield supporters were travelling more in hope than expectation.
Bessbrook student Terry Kennedy, who paid for his trip by picking apples in County Armagh, says: "We all thought we were in for a hammering. There we were, Irish League part-timers, taking on one of the top clubs in England. It was proper David against Goliath stuff."
Supporters who couldn't afford a berth slept in chairs or on the floor of the busy bar and lounges, but not before good-natured banter between fans from east Belfast and the Shankill had turned to fall-outs over politics.
Next morning, the supporters were united again in the cause of Linfield, and buses took them to Maine Road where City players got stick from the visiting fans as they limbered up.
Midfielder Neil Young - ludicrously confused with the Canadian rock star in a recent retrospective on the game - didn't take kindly to the Irish wit and volleyed a ball into the supporters, which only caused even more fury among fans who were already riled by Young's glib interviews in the build-up to the game in which he said if he didn't score three goals he would count himself a failure.
There's no record, however, of Young ever having eaten his words after what Bingham said was the best performance he'd ever seen from an Irish club in Europe - rivalled only by Glentoran's 1-1 and 0-0 draws against Benfica a few years earlier.
Linfield players partied after the game - Franny Lee even offered to buy a drink - but their fans endured a rough journey on the stormy sea crossing home.
"I think there were quite a few supporters who were ill," says Kennedy.
"But no one really cared. It was a privilege to have been there that night and to see one of the Blues' finest performances, though it would have been nice to have come home with a draw."
For the Blues, Maine Road was only half-time in their heroics.
Before the return at Windsor on September 30, 1970, however, Belfast was a city in turmoil, recording its 100th explosion after the onslaught of the Troubles, which also saw widespread rioting on the streets.
The kick-off of the City game was brought forward by several hours on the orders of security chiefs but Bowyer says: "The atmosphere at Windsor was electric. It was said there were 24,000 in the ground but it looked more like a full house to us.
"Unfortunately there were a number of incidents during the match and I remember Billy Bingham going to the Kop to urge fans to stop throwing missiles at City goalkeeper Joe Corrigan, who spent most of his time on the 18-yard line.
"I met Joe a few months ago at a Man City supporters' function and he said that the Blues deserved to win."
And for much of the game, Linfield had indeed looked the part. Striker Billy Millen, who now lives in Australia, scored twice for the Blues, the first coming in the fourth minute after he intercepted a Glyn Pardoe pass-back to Corrigan.
Franny Lee silenced Windsor shortly afterwards with what his own fans acknowledged was a fluke goal, but in the second half Millen put Linfield back in front, though it wasn't enough to knock City out. Malcolm Allison reputedly didn't immediately realise his side had progressed as he was unaware of the away goals rule.
Mercer told the newspapers: "If this was one of the so-called easier draws, give me a hard one every time."
Bowyer still keeps in touch with a number of his team-mates from what he calls "those magical nights against Man City".
And he was looking forward to a reunion that Linfield had organised for this month to mark the 50th anniversary of the City games, but it fell foul of the coronavirus pandemic.
At his last meeting with Bingham some years ago, Bowyer reminisced with him about the Man City games and pointed out that the achievements were made even more remarkable by the fact that just before the Maine Road game, Linfield had lost 5-0 at home to Ballymena.
"Billy had me laughing because he was adamant that no team he ever managed had ever lost by five goals!" says Bowyer.
The City games are, meantime, an illustration of just how much football has changed in the past half century.
For Linfield, who've pocketed hundreds of thousands for beating some of Europe's lesser-known clubs in recent years, didn't earn anything like so much from the City encounters.
The Blues' profits from one of the most astonishing chapters in their illustrious history amounted to just £7,000 which is around £46,500 in today's money.
Sadly, almost exactly one year after the win over Man City in Belfast, tragedy struck two of Linfield's stars of that momentous hour and a half in 1970.
Goalkeeper Derek Humphreys, who had played magnificently against City, was killed in a road crash on his way to the Blues' Euro game against Standard Liege at Windsor Park in September 1971. After the game, Andrews' uncle Alexander 'Joker' Andrews was killed in a bomb attack on a Shankill Road pub as Linfield fans gathered.
Isaac Andrews was later photographed carrying his relative's coffin through Belfast, a reminder that 50 years ago Northern Ireland had more to worry about than football.