Yeah that's true. The only hope at that point would be to copy the search result and plug it into the wayback machine and cross your fingers. If this keeps up, I wonder if the algorithms at Google et al. would start to de-prioritize reddit links over time.
Hopefully those communities that choose to stay dark indefinitely will migrate at least some of their information to external platforms for non-reddit access.
I doubt they'd be able/go so far as to export all the threads, but I'm thinking that it'd be nice if the communities with robust and informative wikis would at least make those available elsewhere. Same with the Fediverse too; I feel like any compilation of information like a wiki ought to be hosted elsewhere for some form of redundancy if possible.