Model collapse comes from using only training data generated by previous generations.
All that's needed to avoid it is to add training data that isn't directly from the previous "generation" of the LLM in question. The thing that causes model collapse is the loss of data from generation to generation, so you just need to keep the training data "fresh" with stuff that wasn't directly generated by the earlier generation of your model.
You could do that with archived material you used for previous training runs. For more recent events you could do that with social media feeds. The Fediverse, for example, would probably be a perfectly fine source of new stuff. Sure, there's some AI-generated stuff mixed in, but that's not "poison."
As I mentioned, the article that demonstrated model collapse did it using a very artificial set of circumstances. It's not how real AI training is done.