Turbo prop and jet engines can pretty much run on anything that is combustible but it wouldn't be certified to do so and therefore un-airworthy
A number of turbines I have flown do list gasoline or diesel fuel as legal alternatives, though with conditions of cleanliness, and for short and recorded durations between overhaul intervals.
BTW I don't believe any imminent demise of avgas. There are tens of thousands of avgas planes around the world. About 1/3 of avgas burnt is burnt in engines which cannot run 96UL or similar
I know it does sound implausible that 100LL would disappear, but back in the mid 1990's I attended the American Society for Testing and Materials (ASTM) meetings for a number of years. This is the forum at which the standards of these fuels (for North America anyway) are discussed. At those meetings, the US Environmental Protection Agency (EPA) repeatedly presented that the industry have a decade to come up with an approvable alternative. If that did not happen, 100LL would just be banned entirely.
It seems to me that we're about 50% beyond that deadline now, with only modest progress. The 2015 end date I have read about, would represent a doubling of the EPA offer. Considering how serious they seemed about this in the mid 1990's, I would not be surprized if they just banned 100LL, and said "We told you so". 100LL burners represent such a tiny fraction of the gasoline users, they do not speak with a loud enough voice to overcome the "get the lead out" movement.
I envision a big rush for replacement aviation gasoline approval in the next few years...