I'd support a fixed term like that, but it would have to be higher than 50 years.
Again, I could never support a system where an author (or musician etc.) can see other people making money off their content while they're alive without them getting their royalty payment.
I think death is simpler, but I'd go for a fixed term of say 100 years if you want a clear date in place, as that's long enough to make nearly 100% sure copyrights aren't expiring in the person's lifetime. 80 would be about as low as I'd go, since not many people publish stuff before 20, nor live to 100.