For consistency, "deleted" things are typically still in the database...they are just marked as deleted in there.
I don't see a field that stores the time it was deleted.
There is a field in that asset table for "last_updated timestamp with time zone". Although that very well may be it the time you're looking for, it wouldn't necessarily represent when it was deleted since it is possible that something updated the asset record after it was deleted.
Sounds like a good feature request.