Oh, wow, that's crazy! I foolishly helped my one Sim to die prematurely. Found out that even though I play on Long, that aging him up to Elder in cas.fulleditmode, the game adds up all the days he's been in play and presto, he died. I went out of that household into Town Management and saw his ghost all of a sudden. What a way to realize a Sim has perished. I was like, say,—what? I won't be making that mistake again.
Can you go back a save? I always use the "Save As …" with the game name (usually my Sims' surname) and a numbering system, so I have them in reasonable order. That way I don't overwrite a save and if need be, I can recapture what I just lost. Problem with losing the Sim I aged up, is I tried to add his additional children into the game. His wife was deceased by then, and I totally made a mess of it. I used copies of this couple (what was I thinking?) of course the added children were forever roommates. Face/palm. Having him die was the capper. I started all over again with this rotation save.