Honestly, not all that much.
There was a time when Mitsubishi was doing pretty well in the US. That was the era of the 3000GT, Eclipse and Diamante – all of which were competitive in their respective segments. Today there's the Lancer Evolution. That's about it. The Outlander and Outlander Sport are decent enough, but compared to their direct competitors they're either dated or bland. Even the base Lancer is no longer competitive. So will Mitsubishi do a Suzuki and leave the US market all together?
Anything's possible, but for now Mitsubishi USA is soldiering on. In the coming couple of years, we'll see the Mirage hatchback and sedan arrive in the US. Both are selling fairly well in overseas markets but it remains to be seen whether Americans will embrace them. The Lancer is actually scheduled for a major overhaul in 2016. It won't be completely redesigned, but it'll receive a new interior, sheet metal, and possibly engine upgrades. Later down the road, the Lancer could be phased out in favor of a rebadged Renault. Next year will be the final year for the Evo, and it'll be sent off with a final edition that'll receive extra horsepower and other performance upgrades.
There's also a possibility that another Renault could be rebadged and sold as a Galant replacement. Both the Outlander and Outlander Sport will continue to see various styling and equipment upgrades, but nothing substantial. Lastly, a next-generation Montero is possible. It's sold overseas as the Pajero and executives are still looking at whether there's a market for it in the US.