It is IMHO completely unacceptable for an aircraft engine to simply stop as a result of an electrical failure elsewhere.
Alternators do pack up, and batteries definitely go flat.
I don't know why Thielert did not fit a second little alternator just for the engine. That's why GAMI developed their "supplenator" - to power the FADEC system. These little alternators have been around for years, and some are STCs for stuff like Bonanzas, IIRC.