After Minsc complained once that his quest wasn't addressed, I moved towards the Gnoll Stronghold (exploring on the way). After getting mauled, I headed to Nashkel for some R&R. After a night of rest, Minsc went ape shit and killed my hero. This was weird for two reasons: 1- I only received 1 warning before this event & 2- Minsc is a good aligned character. Getting pissed and leaving the group is one thing, but attacking and killing seems completely outside his alignment.

Using an earlier save, I made a beeline to the Gnoll Stronghold and averted this uncharacteristic disaster.

I never trusted that asshole! :P Especially after it took me an hour of farting around in #2 before I figured out I just needed to make him mad.

I'll be curious to see if anyone else has had your similar problem.

Minsc is a unique character in this respect. Yes, he is good aligned, but his background leaves him with a serious head wound -- hence his low INT and WIS -- and the propensity to suddenly go berserk. This is what prompts him to go 'ape shit' if you dally in his personal quest to rescue his 'Witch'. This may seem uncharacteristic, but it's a life-or-death rescue mission after all, and (as a character) you must see Minsc as sub-normal because of his injury.

I haven't tried it yet since there isn't really any major reason to do so, but does he undergo a change if given potions of Wisdom or, um, Clear Thought (I think that's the name)?

No. His injury is there, it is real, and no amount of potions are going to alter psychological damage. Besides, on a game level, it is all handled by scripts.

In order to keep Minsc, I had to accept Dynaheir and lose Xan. I don't know if Xan has story development, but I was sad to lose him and his pessimistic quips.

Is Xan gone forever, or is he re-recruitable? Any opinions on the most entertaining NPC's to have in the party (maybe I should do a search for this subject)?

Bummer. That could make for some very funny dialog.

Whether Xan stays depends on your party reputation at the point of dismissing him (he is Neutral aligned). You can always tell if he is gone for good, as he will walk away. If he doesn't, and says he wouldn't mind adventuring with you again (or words to that effect), then he will stay where he is when you dismiss him.

The alignment question at play here is actually a pretty difficult one. As a rule, any creature whose mental capacity is so deficient that they are actually incapable of understanding the moral implications of their actions is true neutral. Thus, in order to be chaotic good Minsc must be sufficiently mentally competent to be answerable for his behavior. The only way we could explain Minsc's uncontrollable violence when raging is by saying that he undergoes temporary insanity and then recovers, but this still presents thorny alignment issues.

The "temporary insanity" explanation only shifts the problem. Even if Minsc lacks the ability to control his destructive tendencies while raging, he still has moral culpability for controlling the anger that leads to the rage in the first place. Using his rage as a weapon in life-or-death combat is one thing, but allowing it to get the better of him in a purely-social situation is entirely another. Being unable or unwilling to prevent his temper from exploding into homicidal rage would be sufficient to knock him down to chaotic neutral.

So yes, up and murdering the party over a disagreement in priorities would be seriously out-of-alignment for him. With that said, the cases of Minsc going outright homicidal in social situations are extraordinarily rare, and in quite a few cases (like the opening "bending the bars" scene in BG2) he keeps it together. As a result, I don't feel there's actually a problem with his chaotic good alignment. However, events like this underscore that his unpredictable nature puts him a hair-trigger away from falling to chaotic neutral.

Xzar is a very entertaining NPC to have in the party in my opinion.

Yeah I accept that since Minsc is touched in the head, his attack was largely a result of some kind of episode sparked by his devotion to the witch.

Well it seems that Xan is gone permanently since he states that his debt has been repaid and walks away (not helped by having a "good" party). I like Minsc (as most) but Dynaheir seems kinda bland. Does she ever become interesting? For the heck of it, I tried to dismiss her, but then Minsc bolts. If an "accident" happens to Dynaheir, will he stay?

It's been a while since I played (planning on starting over in the next day or two) but if I remember Dynaheir was always one hell of a shot and a nice strong arm to keep in the back of your party. With all the talking the other's do it's nice to have one quiet person.

Without mods, do any of the characters in BG1 become interesting? There is virtually no dialogue without mods, so no. However, don't overlook her special ability of Slow Poison. That's nice to have. But yes, Minsc will stay if she has an 'accident', as will all 'other half' NPCs -- If I pick up Skie, I always take Eldoth to fight the Basilisks in Mutamins Gardens *evil grin*.

Yeslick is interesting while you're doing his specific quest. He becomes super-boring as soon as that finishes, though, just like the rest of them.

Minc is a good character.
His main goal is "butt kicking for goodness", thats what he always says.
So the question is: what is evil?
He does not have a definition, but he knows evil when he sees it.
-robbing someone is evil -> kill the robber
-not helping your friend even though you promised to do so is evil -> kill the betrayer

So his behaviour is determined by this rule
- if someone does something evil -> kill him
- if someone needs help -> help him (unless someone need help to do something evil, then kill him)
- if there is nobody to be killed or saved -> sleep, eat, drink, talk to your hamster

So there is only one question left: Why is he a ranger?
He does not seem to have a relationship to nature (except he likes hamsters) and his wisdom is very low (lower than the minimum ranger requirement I guess, but I am not sure). This is strange because he can cast some druid spells (like any ranger).
A berserker (fighter kit) would be much better for him.

edit:
I just had a thought.
If his bahaviour is defined by the 3 rules above and he wants to fight evil, doesn´t this make him lawful good?
OK, those are his personal laws and not the laws of the society around him, but they are laws and he obeys them all the time.
I think of him as kind of idiot paladin. His main task is to protect Dyneheir and he takes this very serious, though his lack of intelligance sometimes gets in his way.