Harry Joe crunches the numbers and, based on the generic balloting right now, says the House is all but gone for the Democrats:

With current polling in conjunction with Bafumi et al.'s paper predicting a Republican national vote between 53.6% and 54.7%, the Republicans could easily gain 50-60 seats from their current 178. Gains of greater than 60 seats also look quite possible. Even in the best case scenario for the Democrats, it would seem that holding the House would be very, very difficult.

The whole post is worth reading -- he's not just pulling numbers out of his ass. This graph, an extrapolation as he concedes, suggests the possibility that the election good be literally off-the-charts bad for Democrats:

Of course, it's also possible that the worst has passed for the party, and that they can rally the base with a health care bill, maybe get some decent economic news, and just suffer a normal terrible midterm election rather than a history-making one.