That's certainly a valid concern; I have never been in that situation so yeah that could be trouble. Aren't there typically local repair centers that do authorized repairs? If not that's a huge oversight even if they only allowed battery swaps. That said, I have a 2006 MBP that is ancient and still works when wired to power even though I can replace the battery it works fine as an email/web browsing headless with a monitor.

That doesn't apply if you're relegating the previous system to media-center duty though.