The next actor who was revealed to come back is Kazuhiko Nishimura, I saw a little bit of Jetman I am easily trying to find more episodes because this is another pre zyuranger sentai series. Also another thing with Liveman it had Yutaka as a villian so maybe in someway they can have his ghost or something like that attack again. Dr. Kemp could have kept himself alive somehow also because of all the science he learned, but it could easily keep him very weak until he finds a way to revive his body. This could be a two parter as well, but high chance that wont happen because Kemp is dead no doubt unless something happened in Liveman near the end because I didnt see the whole thing and dont spoil it for me either.
I'm going to end it there for now because I dont know every sentai series like Dynaman. So I cant say how an episode can go for those series, but overall what I would like to see the most is that Yutaka returns as one of his roles hack could even be for the flashman tribute who knows?