I've seen this happen before as well. I wonder if it would help to have a mechanism that basically removes the user's ability to log in but preserves their data.
'John wants to connect with you', Oh that's cool, wtf?! John's dead?!
>Depending on the privacy settings of the deceased person's account, friends can share memories on the memorialized timeline
I'd love to know which Privacy Settings control this ability, it's interesting they don't specifically call out the relevant option.