Yesterday I asked that about Muji. The short answer for Muji: not doomed yet, but in trouble.
For Forever 21, it appears to be a different story. If you read this, The Failure of the Fast-Fashion Forever 21 Empire – Bloomberg, you see an organization in big trouble, with poor management and poor demand for their product. It is still possible for them to pull out, but I would be surprised if Forever 21 is still a going concern in 2021.