Uni-the-Unicorn!
Hero
Actually, if you read the OP again you will see Hasbro hasn’t folded. WotC is no more and Hasbro puts D&D in the Vault. Additionallly, the OP mentions Hasbro gets litigious about defending it IPThe thread assumes WotC/Hasbro folds completely and some sort of bankruptcy litigation fiasco ensues wherein the rights to the D&D brand are locked in legal limbo and nobody can effectively own/control/use them. That would necessarily mean DMsGuild shuts down. WotC doesn't own the site, but they do have rights to all the products on it, which means those products would become inaccessible/unsellable along with the rest of anything that has the D&D brand, and no new products could be published through it.
All of the tons of 5E material published on DriveThruRPG using SRD and 3rd party content would remain available.
I think the answer to the main question asked here is that TTRPGs would go on, and there would be D&D-alikes created by various third parties, and the ones that are already prominent in the market would be best positioned to grow. But no one of them would ever dominate the market in the way that D&D has, and there would no longer be Dungeons & Dragons as the gateway drug/lingua franca of TTRPGs as we've known it.
That said, it won't happen. "Dungeons & Dragons" the brand is valuable enough that if Hasbro folded and there was an ensuing rights fiasco, a large company (think Disney-level) would step in and pay enough to unravel it and own the brand. Just like there will always be a Spider-man. Even if the company that owns it dies, "Dungeons & Dragons" has enough cultural currency at this point that SOMEBODY would pay enough to pull the brand out of legal limbo and get it into market again - though what the product attached to the name D&D would be or look like would be up for grabs.
Sorry I haven’t read the rest of your post yet because it was clearly based on a false assumption. I will go back and read it shortly and see if there is something to respond to.