Jonathan Bernstein says this is not a recommendation for Weiner just now:

As far as constituents are concerned, that’s where I get to the Gramm example. Phil Gramm was a Democratic Member of the House from Texas. During the first years of the Reagan presidency, Speaker Tip O’Neill believed that Gramm, a member of the budget committee, had betrayed Democrats through a series of actions (Wikipedia has it wrong; it wasn’t simply for how he voted on tax cuts), and tossed Gramm off that committee. In response, Gramm not only switched to the Republican Party, but resigned his seat in Congress, and then ran for and won back his House seat in the subsequent special election.

I don’t recall anyone before or since who did what Gramm did, but I’ve always thought that it was an admirable choice on his part, and that it’s a reasonable model for someone in, say, Weiner’s current position.

The NYTimes has a slew of debaters weighing in on whether the Dems can keep the seat. Polls say this and that, so your free to believe what you want.