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.