I'm wondering if this person forget to pay, someone else will buy this domain and destroy it.
There are also a few sites for the same things like:
Bitcoin.org
Bitcoincore.org
Bitcointalk.org
Bitcoin.it
All of these normally have some way of finding the other sites and other communities so if one site went down for some reason, it'd probably be enough to spread the word about a backup elsewhere.
On the domain expiring, that's very unlikely as there's a lot of communications channels open within the community so cobra would probably find that out and resolve it quickly (or just add years on in advance as is being done now).
As well as the chance someone malicious buys the domain to take the site down, they'd also be competing against those buying the domain for more positive reasons (to keep the site going for example or to stop the domain falling into the hands of a scammer).