btw, if you keep an eye on your engine (if it's not cowled where you can't see it), you almost always get some warning before the tailcone of the muffler falls off.

The warning is in the form of some black oil-gunk appearing on the outside of the muffler. That black gunk is metal filings from the two parts of the muffler rubbing together. If they move enough to rub and create black gunk, you have the beginnings of a problem. In general, if you see black gunk appearing in your exhaust or around your engine, shut down the engine and take a few moments to inspect all your bolts and nuts. Something is working loose somewhere. I've found loose carb bolts, loose mufflers, loose muffler tail cones, and loose engine mount bolts on my planes and on student's planes just by watching for that black goo.