If you're not opposed to using a couple cheats and MCC, it is possible to remove the death trait and then kill the sim again in your presence to have the tombstone/urn appear. I've written up a walkthrough.
kluessims4.blogspot.ca/p/tombstone-recovery.html which includes a video posted by another forum member. It does take away some of the immersion, but you can follow the process on another lot and deliver the urn to your active lot and maybe make it a little more acceptable.