Plenty of AK barrel have seen heavy use and some are pretty much sewer pipes at this point – blown out, dirty and most of the rifling a distant memory. A quick way to check is to take a cartridge of the correct caliber, such as 7.62×39, and put it in the muzzle. If it stops before the case hits, there is hope. It the case hits or even goes into the muzzle, the barrel is pretty much history.
I’m not saying the barrel is perfect but it may still be useful. I built both M70 stubs on their original barrels and they shot good enough – about 8-10″ – at 100 yards fired with iron sights with cheap ammo. Still a fun rifle to shoot though.
If a barrel fails, I would definitely get a replacement and not even bother trying to use it but that’s just me. I’ve known a few guys over the years that proudly built and fired sewer pipe rifles.