Just look at how Cali tries collecting state tax on former residents. Thats exactly the ‘deal’ they would offer. “You can leave but pay us forever for your loss. That way we keep on truckin at your expense”
When it comes to that they will have no bargaining power. Nothing they say, short of threatening force, will matter. This wouldn’t be a negotiations, this would be a unilateral severing of ties. They could build walls around their blue enclaves and extort money out of anyone wanting to leave, but they couldn’t tell Texas, Oklahoma, and Kansas to give them anything.