I am not sure that anyone thinks that Warriors, Wasps or, potentially, Irish fans will just move their allegiance en mass to another prem club. Thats not how any sport works.
What PRL will be hoping is that many will still watch games on BT/TNT/whatever, even if they don't "support" a side. This season I have done just that. Its not the same, but I loved Rugby before I supported Wasps & have a close attachments to 2 grassroots clubs so while Wasps going is extremely painful, I will still watch various levels of rugby without any issue.
I fully understand many others may not feel like that (my wife included!) but I would urge anyone who wants to walk away from rugby, go to their local grassroots club when next season begins, have a beer, chat with the supporters & hopefully you will find a new rugby home.