Noone that I know ok, but of course they're all getting up there in age.
I think Walter Koenig had a heart attack, back in the late '90s when he was playing Bester on Babylon 5 (and what a nice change of character from Checkov that was -- no more Mr. Nice Guy).
(added later) -- Mark Lenard ("Sarak" -- Mr. Spock's pa) is dead.