Now all this content is unhelpful because the sub is private
You could try sending a modmail to see if the mod will give you access to the sub so you can see your own content, or send you a copy of a specific post or comment.
or the original question context was deleted.
One thing to note is that this happened all the time on reddit as folks either deleted their question and throwaway account as soon as they got their answer. Other times folks would ask with their main account but used something like shreddit once a month. So this isn't exactly new to the protest.
When I move my content to its new home, I usually avoid naming the questioner and I briefly summarize their question/responses. This way the content has the added context to be understandable.
If the post is from Feb of this year or older and you forgot the context but want to save the content, you can search for the post in the pushshift torrents - if it was deleted as part of the protest then the pushshift torrent will have the original content in it and you can restore the context that way.
This really bums me out that all this energy and effort has gone to waste.
Additional effort is required to do what I do, but the result is that the effort has not gone to waste, instead folks who want it can view it on the fediverse.
There is something to be said about abandoning and moving on without burning the bridges in the process,
From my POV reddit burned those bridges.
rendering not only your content as useless,
It's not useless, it now serves to move people away from reddit. Remember, with reddit you never know when you will be permabanned - it seems to happen entirely at random nowadays.
but other people's as well
Mostly I've only seen three categories of this.
A throwaway or an account not logged into for a while. The owner if still alive probably doesn't have the access to move it away anymore anyways.
Content that is still present under "[deleted]" - person got hit by a 1k limit or something and missed deleting that before deleting the account.
Content from a mod, who has't moved off yet as they're trying to hold onto the sub for the protest.
I figure I'm better off moving my content with context anyways, since that prevents the person in 1. or 3. from coming back and confusing the context.
The other thing I do when commenting is quoting extensively, that way the context is clear from my own comments.
To stop scrappers, offer the same pricing as API to anyone using the web version of reddit. (New or old doesn't matter.) Ordinary users have to pay, per thousand comments, to see reddit.
Actually, do the same thing with the official app (since folks could otherwise use it for free and take screenshots or something). But leave the ads in too.
As others have said, PDS is a good choice as it avoids a need to use the API. (It does depend on old dot reddit dot com however, but that's not going away tomorrow.)
In short you need to request and get the GDPR/CCPA archive from reddit to make sure you wipe everything. (Some folks can live with just wiping out their top posts and comments however, for which PDS is perfectly fine.)
The downside is that afaik there's no way to feed that archive to PDS. You'll need to use an API using script like shreddit to edit everything.
Reddit admins using that "feature" to post under other usernames perhaps? I dunno if there's a way to check but I wouldn't be surprised if these folks were not actually subbed to the sub that they seem to care so much about.
TLDR reddit might not be restoring data that the user deleted, but there are some funky cases where it's easy to miss stuff when deleting manually. Which is exactly why Update #1 is so bad - it's basically impossible to delete everything without reddit's help.