Personally, I just can't imagine CBS hiring him if they thought he really was only going to be there for 1 and a half years. That just wouldn't make any sense. It takes time for viewers to adapt to a character. If he was really there for only 1.5 seasons, then his character would barely be established before he left. Every impression I've gotten is that he's definitely a long-term character. I really, really doubt LF is going to leave, at least after only 1-2 years. From interviews I've read, I got the impression that part of the reason he joined the show was because it was stable and fit with his family life, probably at least in part because he has a very young child. I don't think any of that would change that much in two years.