MATE is separate from what Mint is. the solution is easy. I have done what is in this thread, and have done what you call changed hostnames, and it crashed mate because caja kept autostarting. so i apt-get install --reinstall caja, after apt-get remove caja and MATE is gone from session list at login and from my gnome desktop with cairo dock. the best thing to do is reinstall mate, login with an active session that works or by terminal and become root or use sudo:
apt-get install --reinstall mate-core
there are two other features, run the one for the desktop environment and the one for the MATE extras. a quick command reference is here.
if you have any problems, use apt-get remove, then perform apt-get install, and don't use --reinstall there are 3, do them in order one by one as apt var will lock and only one will work at a time.
it takes 5 minutes and all is restored without files being lost, icons being lost etc . . .