Executive dysfunction has kept me a serial lurker at the edges of fandom for at least 20 years. Tumblr has been great for me bc it lets me curate content instead of producing it. I don’t have to have a prolific presence, I can throw out an original thought or edit or fic only occasionally and still be heard, whereas my lj was a barren wasteland. I hate what’s happening. I don’t want to go back to filling the occasional kinkmeme while feeling like an outsider.
Tumblr has, for better or worse, shaped a different kind of engagement with fandom together with progress in technology that made us have so much fun with moodboards, gifsets, imagespam, etc. I don’t think people will easily leave this, but rather transition and try to find somewhere that will offer them something similar, or something slightly different without really losing what they already had.
We’re likely on the edge of a new phase, and it will take a while to find our bearings again, but it’s likely you’ll be entirely free to do what you’ve done till now, either on tumblr (but sans what’s out of their ToS), or on any other fandom friendly tumblr-alike social that gets created (pillowfort, to name one). Even different sites with different formats can be tweaked till they come as close as possible to what you were used to before. It takes patience though.