Quite a few are now gone...
d Roger C. Carmel - Bruticus, Cyclonus, Motormaster, Unicron (post movie)
d Phillip Clark - Dead End, Tantrum, Abdul Fakkadi, Auggie Cahnay
d Rege Cordic - Menasor, Quintesson Judge (movie)
d Scatman Crothers - Jazz
d Walker Edmiston - Inferno
d Ron Feinberg - Headstrong
d Ron Gans - Dragstrip
d Linda Gary - Chromia
d Ed Gilbert - Blitzwing, Thrust, Shawn Berger
d Jim Gosa - Abominus
d Johnny Haymer - Highbrow, Swindle, Vortex
d Stan Jones - Scourge, Pounce, Weirdwolf, Lord Zarak
d Aron Kincaid - Sky Lynx
d Bert Kramer - Computron
d Chris Latta - Starscream, Defensor, Reflector, Skullcruncher, Wheeljack, Sparkplug, Snake
d Don Messick - Gears, Ratchet, Scavenger
d Jeff McKay - Fireflight
d Tony Pope - Wreck-Gar (post movie)
d Ken Sansom - Hound
d Tony St James - Blot, Brawl, Cutthroat
d Robert Stack - Ultra Magnus (movie)
d Lionel Stander - Kup (movie)
d Orson Welles - Unicron (movie)
I guess it has been about 30 years now, but damn that's a fair chunk of the original cast gone now.
At least all the JP characters can get all new VAs, and very few of the US cartoon characters show up to even worry about.
(
from my page here)
A redubbing of the JP series could be a good (and cheap) way to sell some future Generations toys - the Generations line could feature a heap of JP Gen1 characters that were never released by Hasbro to begin with.