Let's assume this was the 2012 map. Romney would also have to win the national PV by 1% or so to win the election. For now, let's assume a 2.5% uniform national swing:
Romney/Ryan 49.65% 295 EVObama/Biden 48.51% 243 EVIf you apply the same swing to all of the 2012 Senate races, only Heitkamp and Tester would actually lose, but there would be recounts in WI, IN, OH and VA, where the Dems would all have <1% margins of victory. So, surprisingly, the Senate would still be
53D/
47R.
In the House, it's pretty clear Republicans would gain seats, and this uniform swing would give them the nationwide PV for the House vote as well. Let's assume they pick up 8 seats instead of losing 8 for
250R/
185D.
How would Romney govern with a split Congress? Would he be popular? It seems pretty clear that a Dem senate wouldn't let him touch Obamacare and would be unlikely to sign off on significant tax cuts. On the other hand, he would have a PV win under his belt which could help on the legitimacy front. And in 2014, while it's unlikely Democrats would make Senate gains (their only real targets would be Collins and maybe McConnell), it's also quite likely that, as the opposition party in a midterm, they would hold enough of their own seats to retain control. Also, given the 2016 map, it seems unlikely that Romney would ever have a Republican senate to work with unless he won reelection in a blowout.
So if we assume Scalia still passes away in Feb 2016, it's presumably the same scenario as we saw last year, but with the parties reversed and the Dem senate refusing to confirm any Romney appointee until after the election. Would this help or hurt Romney? Would he face a more consolidated populist challenge in the Republican primary, especially given that he would have been unable to repeal Obamacare or pass any abortion restrictions with the Dem senate? Could he come out of this significantly damaged with the base or even lose the primary? Which Dems would run? Obama would be young enough to try and pull a Grover Cleveland if he wanted to.