The annual means it was airworthy in May, that's all.

It can go until it stops, the idea is to overhaul it before it stops.

As pointed out, the airframe value if it needs an engine overhaul is "not much."

One nav radio. Welcome to the joy of intersection holding.

Compression testing is a black art. Continental says you can get down to 60 if you do the test per their procedure. Then you need to figure out where the leak is.