Are there other known uses for the Rotax other than aircraft?
Assuming we are talking Rotax (which hasn't been confirmed as yet) and further assuming we are talking about the Rotax 912, which has been most plagued by this theft vague:
One could of course use them in a boat, or to drive a generator; but there are cheaper, simpler, less delicate engines for such applications. IMHO they'll never command more money than in the application they were meant for.
Neither do I much believe in their value when marketed as spare parts: major overhauls of these engines are rather exceptional, hence demand must be limited. Except perhaps in Eastern Europe - where I suspect most to go anyway.