Did it yesterday, there seems to be an odd bug with WoW on Lutris and when you use alt-tab to go back to the desktop it can crash the whole session. Happens maybe one out of ten times.
I just ctrl-alt-F3 to a terminal, ps to find the pid and then kill pid to get rid. If it's refusing to budge i'll kill -1 the session, i've found that works with more stubborn problems.