It probably would be a more effective campaign for subreddits to have their users wipe all their old comments (older than 1 year) than a temporary blackout for a few days.
The site would likely be better if they did, as it’d incentivise heavy moderation and on site content production, but that’s not /r/all at all.
There's no reason to prop them up. The information will be rebuilt quickly or it won't.
If people were really committed, they could "unionize" and have a centralized party which held access to their comments, but that would probably violate their ToS and would not set a good precedent for an open and free internet. Not to mention, Reddit could easily just block users from modifying/deleting old comments.