There's been a lot of negativity for how the Republicans are doing so far in redistricting, with experts predicting 5 seat losses in both California and Illinois.
It could be that bad, but only if the roof falls in. You're talking about the Democrats upper limit here. They'd have to win every single competitive district in both states. The roof fell in with the 2006 election. And then we had an earthquake, fire, and flood in 2008. Yet these were two states that Democrats failed to get many of their targets.
I looked at the states that have either completed redistricting or almost have and calculated how each party will do. I calculated the odds for each district and assigned them a numerical value with 1 being safe, 0.8 likely, 0.6 lean, and 0.5 toss-up. One party could lose a bunch of seats that I predict as likely, but the odds are that they'll keep 4 out of 5. The numbers don't add up because some states, e.g. Illinois, are losing seats, while others, e.g. Texas, are gaining seats. Keep in mind this doesn't always reflect candidates, as some are unknown. That and election conditions can change this.
The numbers are relatively negligible right now. Even if you assume the worst for Republicans and add a few you'll get the Democrats gaining around 8 seats. That's tough but not a great dent into the Republican majority. It'd result in a 233-202 Republican advantage.
But there are still a bunch of states to go. Republicans control redistricting in Wisconsin, Pennsylvania, South Carolina, Tennessee, Ohio, Michigan, Utah, Georgia, and North Carolina. Democrats control redistricting in West Virginia, Maryland, and Massachusetts. The remaining states are small or have a split redistricting. Republicans do control redistricting in Florida but the Fair Districts law will limit their gerrymander. That said, they still will be able to skew the districts somewhat.
What's immediately noticeable is that while Republicans have few opportunities in states they control, they also can prevent losses. Republicans have 4 congressmen in the three states the Democrats control and it'll be difficult to gerrymander 3 of them out of office. Simply put, it's unlikely the Democrats will pick up more than a seat in a handful of states, while Republicans will pick up several and prevent losses. The Democratic opportunities have already been redistricted.
That means that Republicans should be able to sail to at least 233 seats. This could go lower if Obama wins big, but re-elections don't have long coattails and the 16 additional seats is likely too long. Of course Obama might squeak out a win or the Republican could win. Usually when a new President is elected his party gains seats. Thus, a Republican victory would push it the other way.