I recently had an issue with my p-trap on a bathroom sink and ended up replacing the whole unit.

As I was doing so, I noticed that the pipe leading to the wall for the drain was crumbling and/or thin on the end of the pipe. I was able to make a tight seal to the p-trap, though I'm still left with the concern if it causes further issues. There is only about an inch of pipe coming from the wall.

What would I be looking at if that pipe had to be replaced? Would they have to knock out that section of the drywall to replace the pipe? Any thoughts on anything else that might be involved or possibly a rough estimate on total cost?

Thanks in advance.

Probably had /was a brass pipe. Common in older homes and causes headaches when it corrodes. I would leave it alone. There is a threaded compression nut to tighten against the p trap arm? No leaks? You are lucky. Ultimate solution is to open the wall, replumb with PVC and a female coupling.
Cost depends a lot on where you are located. I have used epoxy and metal tape to stub out a PVC pipe and coupling. So far has lasted 3 years with no issues.

What would I be looking at if that pipe had to be replaced? What material's the pipe? Chrome? Copper? Galvanized? Is a solder joint involved? Let me know, Tom