My son's 00 Civic EX D16Y8 170K miles has oil leaking into the coolant it also has over heated. It still runs and gets good MPG. I've read how the block is porous or head gasket maybe bad for the oil to get into the coolant.

I'm torn between trying to replace the head gasket?

Replace the engine (rebuilt)?

Run it until it dies or has more serious issues?

The body is OK and has some hail damage. Basically for a 16y/o car it isn't bad.

Any thoughts or suggestions?

 

As much as I hate to say it, you need to read the rules. This is an entirely opinion-based question, and you need to make that decision.

 

head gasket ~350
engine ~2,000

hmm

 

If the engine has been severely overheated, then replace it.

Otherwise, compression test the cylinders and do a leak down test on cylinders with low compression.