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"It’s hard to imagine an implosion of that magnitude leaving so many large pieces, including the wires, intact."
The tail section was mounted to the structural support system - not mounted directly to the pressure hull assembly itself. Some cables ran from the tail section to the pressure hull where, for some of the cables, there appeared to be a bulkhead-type fitting situated at the top (12 o'clock position #) of the pressure hull near the front titanium ring. There, cables passed through the hull. Cables also ran to various external (outside the pressure hull) components of the submersible.
(# One of the photos in the news, of Stockton Rush sitting inside the pressure hull, showed a cable run at the 12 o'clock position, described. Yet, I remain uncertain about, exactly where all the cables entered/exited the pressure hull.)
In the photo (reply 50) that reveals the starboard tail section view and components, there are a few WHITE rectangular shapes that are not deformed.
"Is it usual to use epoxy in submersibles?"
There are many types of epoxy for marine applications. A lot of Research & Development goes into testing and nudging epoxy compounds toward a finished product that works within a range of parameters, including pressure. Some applications, are for encapsulating electronics; and such an application is probably the case for some of the components within one or more of the aforementioned WHITE rectangular shapes that you see in the revealing, starboard view of the tail section.