And as far as continuity, last time we saw Sara she made it clear she was happy, without him. Better off, actually. Things ending was for the best. So in true CSI stupidity, it makes complete sense for Grissom to find her in the middle of the jungle in Costa Rica so they can make out.
OK, you'll never count me in the camp of folks who favored a relationship between Grissom and Sara. But I think you're missing some points that the writers have made. It was just a few episodes ago that Catherine talked to Grissom about having a family in Vegas . . . or, at least, a work family, and Grissom replied to her that maybe it was time to up the ante. I thought it was clear then that he was going to make some choices about making "family" mean more in his life than just his work family.
I also think that Sara letting Grissom know that she was OK freed him, but not in the way that most people thought. It signaled to him that a relationship between them was not about need (Sara's, specifically), but it could now be on more of an equal footing because of the work she'd done to resolve things for herself and her feelings about him. So I think it actually made sense for him to return to her.
People are complaining that the Grissom we see now isn't the same Grissom we knew at the outset. Of course not. No one is static in life (or, at least, no one with a healthy mental/emotional outlook). And Grissom has made some significant choices to be a different person. We've seen evidence of that throughout the series. And, the truth of it is that he has aged. They all have. Eight years somehow seems like a whole lot more. I can understand the complaints about the writers supposedly not getting the characters, and to some extent I agree with that. But I also think that the changes we see are not entirely without foundation. If I think about it, some of it makes sense just based on the life experiences people have had . . . and time.
Anyway, onward and upward. Like it or not, Grissom is gone. Part of me is very sad about that, because it's the end of an era. William Petersen was the entire reason I started watching "CSI" . . . and he was the main reason I
kept watching. For me, Petersen is a big part of what made "CSI" special and set it apart from the rest of the pack even after forensic science became the latest fad on TV (thanks to "CSI"). Yet a part of me felt that, as Grissom said, the time was right for him to go. And maybe it is possible for me to enjoy the series without him. Time will tell.