There is the Rejuvenation potion — that seems to set your sim back to the start of a current life stage and keep them there for a time. (I haven’t tested it myself, just read it in Carl’s Guide) Just have your sim keep drinking it (kind of like the elixir of the Philosopher’s Stone in HP).
As for my common elder deaths, I guess I will still have to keep a close eye on them! At least now I have necrocall and de-deathify for their children to use to resurrect any beloved elders who kick the bucket suddenly).
