Given
A. where the teams is (good start but still a year or 2 off from serious contention)
B. contract situation of the players. (both Lin and Bev are still on 2 more years of contract. Lin's above average paid but not by a lot, Bev's a huge steal)
C. the likilhood of a star caliber PG coming through the door without gutting the team (like... 5% ?)
It seems pretty obvious that baring unforseen events Lin's going to stay next year, and this question would sort of play itself out, either he gets better , or he doesn't, if it's the later it's obvious that he'll probably not play out his contract in Houston, if it's the former .. then the question is how much so. if he gets to like... a 17-18 PER .140+ WS/48 type guy, I think he'll almost surly play out the contract, if it's more like 16 PEr .120ish WS/48 type guy, that's a tougher question to answer.
He can get to the rim well and finish reasonable well, his 3 P shot is no longer as much of a liability as before, defensively he seems fundamentally sound most of the time, the missed rotations happen, but it's hard to seriously tell if that's totally on him or not.
As Rahat pointed out, the biggest thing for him is really the ball handling, a lot of his other problems stem from this too, if he gets this down, he should be fine.
Looking at the bigger picture, the projection hasn't changed that much as it was before the year, only that we got off to a better start than expected (but to keep things in perspective, we made the playoffs by 1.5 game and health was really on our side in comparison.) This was always going to take a couple years, Lin's play this year suggest he's clearly a NBA player, the question remains if he's a legitmate starter on a good team. will be answered next year, which wasn't unexpected either when you look back and consider that he was a guy coming off a big injury on a totally new team (literally, the whole cast changed.)