I heard that somewhere in the code of a hidden website is problematic and reveals its real IP address, in other cases LE seize a server and discover some other hidden sites on it, and take all of them down, BUT provided that the private key of a .onion domain is only in the hands of its creator, and the creator is NOT apprehended, are they not able to reclaim the .onion domain and continue their service? (So why do they not do this?)
When a hidden service is seized, 'they' (the LE agency in question) are in possession of the private key. Either obtained from the server or from the operator.
I imagine that in many cases they are also in possession of the operator, and have some leverage to convince the operator not to continue.
Is it possible (and has happened) that a 'seized' domain is also run by non-LE. This creates the situation where the server you hit depends on your introduction point and/or even time of day.