Unless you're Jerry Miculek, I don't think you will ever wear out a barrel.
You could do "baseline" accuracy tests for it right now, to establish its "close to new" level of accuracy. Store these targets away and every few years get them out and compare them to its current capabilities. When you see a marked drop off in accuracy, you can worry about it then.
My guess is that any loss of accuracy will be more due to age of the shooter than to wear of the barrel, but you may be setting up a future excuse to buy a new gun!
