Re. the Rotax as a reliable water-cooled engine:
I can't speak for other variants, but certainly the 914 in my aircraft is still partly air-cooled - specifically, the heads are air-cooled while the cylinder walls are water-cooled. In the event of a coolant leak, the engine will still run for a finite amount of time - can't remember exactly how long it says in the manual, but it's long enough to get to an airfield unless you're somewhere pretty remote.
FFF
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