I don't know all the answers - nor have any of my own alts ever been banned so I did not have an occasion to look until now, but I see where the account is not removed, and in fact can be un-banned later. Here's an irl example: https://lemmy.ml/u/sagxd (which we can see ourselves without an account on that instance - plus it is also visible from elsewhere e.g. https://lemmy.world/u/sagxd@lemmy.ml). You can read the story behind that incident in https://lemm.ee/post/45204357.

Most of the time how it seems to show up in the modlog, at least whenever it happens from lemmy.ml, is a slew of being banned from every community on the entire instance. Although there does seem to be a modlog entry to do differently (note the presence in the pull-down menu of "banning from site"), which despite not seeming to be (commonly? ever?) used from lemmy.ml, is indicated as often being used from other instances.

In particular I don't know if a banned account can give or receive voting - I think I've heard people say both ways. I've saved your post and I'll check back in later to see if someone can say with some actual knowledge what is going on!?:-)