I don't like sticking teams back where they failed once. It's like getting back with an ex-girlfriend.
I think you have to understand how they failed, though. This was no break up because of loss of love. They pretty much sold out their 15000 seat arena until the end, but there's not enough income from just tickets. They needed a bigger rink and Corporate deals.
They left Quebec in 1995 - before the Salary cap. Canadian teams had to pay much more for players because $1US was .70. Because of that and the escalating salaries the team began to struggle financially. Now there's the salary cap and the Canadian dollar is .92 and has been even in recent years.
The team couldn't get corporate sponsors because the Quebec economy was in turmoil. This was in larger part because of the seperatist movement that lead to the 95 referendum. Nobody wanted to invest in Quebec because of that uncertainty. It's a lot different in Quebec. As already stated, Quebec City is already building a 400 million dollar modern arena just on the hope of a team. The also have a huge deal with Quebecor media for the naming rights on the arena that increases if an NHL team is there.
As for your idea of fans fading in interest if the team is losing - you can still buy Nordique merchandise in any sports or souvenir shop in Montreal and the team hasn't existed for almost 20 years. I think that says something.