Need unbiased opinions on a sticky situation

In order to keep this as unbiased as possible, I won't say who I am in this situation - although I'm sure some will guess anyway (this is hard)

There are two friends - they have been close friends for over ten years. Friend A invites friend B to start playing an MMO with them. Friend B does, starts to enjoy the game, ends up joining friend A's guild and starts becoming a part of that community. Things are going well, both friends are enjoying the game and how things are going. This is the first time in a while that friend B has had the chance to successfully integrate into a group setting and is encouraged by the social progress. Friend A is glad for friend B - thinks friend B making a lot of healthy social progress in being able to trust people enough to talk in group conversations and just relax a bit which is good for them.

Things are going fine until at some point the guild leader kicks friend B out of the group. When friend B asks for the reasons they are given no reason - except cryptic remarks referencing things friend B did that were categorized as harassment. This is out of the blue - friend B has done nothing at this point to warrant such actions (their interactions in the group have been surface level and polite) - and friend A is 100% positive that friend B did not do anything, as it was pretty clear friend B was integrating well, and friend A knows friend B well enough that they know they wouldn't do anything like that. It's clear that someone, for some reason, spread some sort of rumor about Friend B, or that the guild leader didn't like Friend B and wanted them out because of a personal dislike.

Friend B has been struggling with depression, so when this happened it hit them hard and was a very confusing and hurtful experience, especially because the guild leader was very callous and insulting before kicking them. They came to friend A in tears, hoping friend A might be able to figure out what happened, or do something since Friend A is friends with the co-guild leader.

Friend A tried to ask questions, but got rebuffed. None of the higher ups will talk about it. All the other guild members are surprised to find friend B is gone and doesn't know why as friend B was fairly well liked.

If you were in Friend A's position what would you do at this point? Would you stay a part of the group and try to move on with life, continuing to socialize with and be friends with people that dealt your good friend such a serious and uncalled for blow? Would you tell them off and leave the group?

I'd find a new group if people acted that way, because they will turn on you next.

I've no time in my life for catty behavior, so it's easy for me to walk.

I don't think confrontation is necessary because it really solves nothing, as you've already tried to get an answer and didn't.

There are other groups out there, maybe next time don't include your friend again if it will be an issue. It was a nice gesture

but friends don't need to be joined at the hip.

If I was friend A I'd be demanding to know the real reason why friend B was kicked out. If the guild leader couldn't give me a plausible reason I would tell them what I thought, start my own guild, let all the other members know what happened and invite them and the mistreated friend B to the new guild. If bullying has happened it should be stood up to.

things friend B did that were categorized as harassment

Such as... ?

Guild leader would not say what. They only spoke in vague accusations and never gave specific reasons.

If you were in Friend A's position what would you do at this point?

Have you seen the movie Role Models?

Check it out