Hello, yesterday I was playing a challenge with special sims and the zombie sim died (I didn't realize the exact moment since I let the sims take care of themselves), I was looking for the grave and it's not in the lot, it has disappeared! I bought the phone to call the grim reaper and it says that there is no sim in the lot that I can recover, can't I do anything to rescue that grave?

You should be able to use the batbox to respawn the grave, just pause the game, summon the ghost to lot, make them selectable, and then the option should appear for them on the batbox.