The Knicks aren't going to let Lin walk. They have around $7.5m invested in their two PGs so far, in Felton and Kidd. They're going to have to match the offer sheet and just deal with paying off the poison pill third year.
In three seasons, if they're over the tax line, it's going to cost them a extra $20m in luxtax, which is going to hurt big time. They are heated at the Rockets, and that's why they're playing games like having their GM disappear so the clock to start on the matching time period will be delayed.
They just can't let the guy walk. He's way too valuable to them off the court.