To do so the Oaks will have to beat Italy at Exeter's Sandy Park on Sunday, just five days after fighting back against Canada to record their first World Cup win since 2007.
"They've earned the right for a beer," Howells said. "There's a limit. They'll have a beer but it won't be to a great extent.
"It'll be in the team room and we'll have control over them."
The players could be forgiven for struggling to contain their celebrations after a pulsating contest at Leicester City Stadium, which was settled by Romania's Florin Vlaicu kicking a penalty three minutes from time.
Canada had looked on course for victory after tries from DTH van der Merwe and Jeff Hassler gave them a commanding lead in the second half.
Two tries, however, from captain Mihai Macovei brought Romania to within one point of their opponents before Vlaicu held his nerve from the tee to seal a dramatic win.
"Did I think it was over? No, and I say that for one reason," Howells said.
"We said if we stayed within 14 points going into the last 20 minutes, we knew we would have a chance to play the way we wanted.
"I think you saw that. Canada's wide game started to fall apart in the last 20 and it gave us an opportunity to play the way Romania want to play. I never gave up."
Italy will be heavy favourites to win the final match, particularly with an extra two days' recovery time, but Romania targeted these last two games and will arrive full of confidence.
"It's the semi-final won, now we play the final," Howells said.
"There is still an opportunity, in rugby anything is possible. Against Italy the players understand they are playing a tier-one nation and they have to lift their game."
Howells added: "It gives us the opportunity to get two wins and qualify automatically for Japan. That's something that has never happened for Romania."
Canada's campaign is over and it is the first time in their history they have ended a World Cup with four defeats.
Kieran Crowley's side took a losing bonus point from a brave performance against Italy last month but they crumbled under pressure in the second half against a physical Romanian side.
"What do you think it feels like? It's horrible," Canada captain Jamie Cudmore said.
"The guys are extremely disappointed after working so hard.
"We came up second best against a team who I thought we were better than. The boys are extremely disappointed and I'm just as gutted as they are."
Manager Gareth Rees added: ""To echo Jamie's comments, it is totally unacceptable to finish a campaign with that performance, for 30 minutes, and to finish a game like that.
"I would like to apologise on behalf of the players that we let those people down. That's the way it is, that's international rugby, we didn't play well for a patch."
Romania's win also had an emotional element to it after captain Macovei said the mother of forwards coach Marius Tincu had passed away this week.
"We want to thank Marius Tincu because his mother died three days ago and he decided to stay with the team," Macovei added. "All of us had our thoughts and hearts with him."
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