Talented artists are, yes, sometimes more than a bit difficult to deal with or maybe even a little handicapped in their "basic human being" skills.
There was a thing for a while where comics I liked kept decaying from 'brilliant' to 'weird' to 'pointless' and then they'd stop because the artist had been diagnosed with an acute need for inpatient mental care. It happened several times.
I have no idea what happened to David Sim. AFAIK he didn't get better. Uncle Ghastly dropped comics and got into music (but I don't know what became of his band, sorry), Michaels changed art genres and became a novelist. A couple of others eventually got better and got back into comics, even more brilliant than before but very very different in tone, theme, and context than their previous comics. And IIRC, drastically slower production schedules. Brilliant writing, gorgeous art, glacial production....