As long promised. So, go on, what do you have?   Lifeboat (1944) has 10 castmembers listed on IMDB, all of them have confirmed death dates (the last surviving actor would have been Mary Anderson, who died in 2014)   I was going to say "well, obviously, Swimming to Cambodia counts" - one actor, and he killed himself 15 years ago. However, there is archive footage in the film taken from The Killing Fields, and Sam Waterston is still with us and being mildly entertaining in mildly entertaining sitcom Grace and Frankie.   The travails of us failing to clarify if everyone from 12 Angry Men is dead can be found here. In short: almost certainly, but we can't prove it.   So what can you prove DL?