The numbers need to be dwindled. Period. Myco can be brought on by stress and being kept in huge groups of sickly populations cannot be healthy and is probably exacerbating the situation.
A rat rescue would be ideal, but they're usually overtaxed and spread thin as it is. Much less taking in a large group of animals who all need months of care and costly surgeries. Add in males who cannot be housed with other males and you're making it double difficult for them.
I love rats, I own rats and have for years. But this is not a healthy situation.
No, I don't think they should be fed to snakes. Not only because they are, by and large, pets, but because I don't think feeding rats with cancer is wise anyway.
Yes, the rat community did help shuffle hundreds and hundreds of rats to shelters after the Hoarders case, however, last I had heard, many of those rats were still unadopted today and living at rescues. I don't necessarily feel that it's any healthier for a rat to live in a rescue for years than I do a dog or cat.
I think humane euthanasia at the vet is wise for a number of the sickliest rats. (for the record, at my workplace, we gas the rats, then do the heart stick.And they're put in with the communal cremations when they're taken away)
It's great if your numbers have been halved, but if you recently had 80+ rats, that's even more concerning.