PhilB over on the Ducati Monster Forum has over 200k miles on his 2V 900 Monster (same engine).
There are several other examples of >100k miles 900 2v motors.
As was stated above, maintain valve clearances and replace belts when due and the engine will outlast the other components of the bike.
2012 Ducati Multistrada 1200S Touring
2013 Husqvarna TE310R
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