Should easily get 10-15k hrs with normal maintenance and proper operation. Things will go wrong, like water pumps, electrical stuff, torsional couplers, injector pump, leaks. But base engine should hold up.
I know of one 220 that blew up, but that was on a planing charter boat and when loaded, he would literally run it at FULL power for hours on end. Even that one lived for I think 7k hrs til the head cracked itself to bits, spewed coolant and cooked hard.
In trawler service, it is similar to the engine in the older Dodge pickups. Lots of running at 2-3gph (easy) and they easily made 500k miles, with some many more. And when finally retired it was the truck that became a POS and the motor was fine.
On a truck, 500k miles at an average of 30mph (guess there) is about 17k hrs.
Get someone to check them out (rpm, temps, blowby, oil samples), make sure you can get to everything access wise, etc.
You will have to do a LOT of cruising to wear them out. And if you do have a big problem, it is one of the easiest engines to work on, and worst case one of the least expensive to replace.