They were a part of Tree Hill and at first I thought the show wouldn't be the same. There are still times I miss them, but that's because I am not fully sattisfied with the ending they wrote for them. They just ride off in their car, without saying goodbye to their friends. They were best friends for alot of years, and suddenly they leave without having a final word with their friends. That was written realy lazy imo. But that's the only thing I hate about it. Peyton and Lucas were important, but their story-lines were written realy bad the last 2 seasons. They were just out of drama with those 2 characters. So I thought it was a good decision to write them off [ again, the way they wrote them off was really bad ], so the show could welcome some new faces which I really fell in love with.
I do hope however, that at least Peyton with return for one episode to have some scenes with Brooke and Haley to have a proper send-off. I don't want the last scene that I remember about Peyton being a sad and bad written one, since I realy like the character. Her character deserves proper closure. And just explain Lucas not being there; by letting Peyton say he is sick or he got a visit from his mum.
BTW, I know it's not the subject of this thread but I do hope we get to see Debb again! She just vanished in season 6!