I'm talking about his family.

I know that you get 15.5K XP if he takes the peaceful route, but what if he goes to court, what then?

Are there any changes in stats, personality, etc?

There are no stat or personality changes. The only practical consideration is that if you release him from your service (when he asks if he may stay with his wife), then he will no longer be available... period. If you give him one day, you may go back for him. You can also tell him he must uphold his promise to you, which means he doesn't get to spend time with his wife.

There is an incidental consequence of going to court, if I remember correctly, that his children will no longer speak to him. But that is neither here nor there, since once it's over there's no reason to go back. It's a bummer r/p wise, but it won't affect anything.

Yes, the whole thing was a bit weak from a RP standpoint, but I kind of like the darker outcome, even though it was unintentional. Thanks for the reply.

I don't think it's an accident that the most powerful Good NPC in the game is the hardest to keep in your party, between his family quest and the fact that he'll leave you if you don't stand up straight enough.

I'm assuming that even if you lose him permanently in SoA, you can still get him for Throne of Bhaal, right?

I don't remember Keldorn being difficult to keep. His personal quest is basically just running back and forth, talking to people. Want to keep him in your party? Just don't let him leave at the end of his quest; he's so honorable that he'll hold off on spending time with his family to fulfill his obligation to you, even if he JUST started repairing his relationship with his wife. When adventuring, just don't be really evil (or spend the money in temples if you decide to start slaughtering innocents). I'd say Aerie is more difficult to keep, with several possible conversation branches making her bail.

As far as I know, you can pull anyone except for Yoshimo into ToB. I'm not sure how the game handles it if they died and you kicked them, though. I imagine you can still pull them but I haven't tested that.

All hearsay, I guess, as I've never played using Keldorn so far. I know any good character will leave you if you have too low a reputation, but I've been led to believe that Keldorn will also ditch you if you ever turn into the Slayer or if you side with Bodhi in the guild war (which I generally do, as I have a much more visceral dislike for organized crime than I do for fictitiously evil creatures, and I know I get to face Bodhi either way). I don't know of any other NPC who behaves that way.

Correct on both counts. Here are the party critical Keldorn events (not counting reputation) to watch out for:

Keldorn will leave the party if you...
** Attack Sir William
** Side with Cowled Wizards against Valygar
** Rob temple of Lathander
** Refuse to help Renfeld
** Side with Bodhi

Keldorn will leave and attack the player if you...
** Attack Valygar
** Attack Adalon
** Give Adalon's eggs to the demon in Ust Natha
** Attack Drizzt
** Attack Svirfneblin village in the Underdark
** Turn into Slayer (UNLESS Mazzy is present, who takes precedence)

I assume that only applies if you do it voluntarily, rather than the scripted first change?

I think so. The first change is cut-scene triggered, so Keldorn's interjection script won't react.