In Alt on a Private C of A you can run an engine until it falls to bits. As you say, this is subject to a 50 hour check which will involve an oil change (as it should now and I think a compression test has to/should be(?) carried out. This will ensure that all the cylinders are contributing their proper share of the work (within specified limits). So as long as your compressions are greater than 65/80 and there are no shiny bits in the oil or oil filter then you can keep running the engine. If you tell A & C which engine you have, I'm sure that the details of the specific tasks will be forthcoming. My 50 hour checks usually coincide with the Annual so I don't know how much they cost.
It will eventually wear out of course but regular oil changes and regular flying should keep it sweet. I had a 2,500 hour Continental O-200 in an Aerobat and, after a top overhaul, it was sweet as a nut. On the other side of the coin, I know of an Arrow that was flying around with a 3,500 hour engine. It sounded like a bag of bolts and I wouldn't have used it as a boat anchor but it did work and it was legal......