I think it's either zero or practically zero, as in the price of ETH slides so low that they have to fix it at that point to keep the scam going.
Think about the incentives from their point of view.
They already have their entire security budget forever now. Just never let the staked ETH unstake. With the ETH they have already staked, they can secure their blockchain forever, just so long as everybody buys $100 of hard drives every month, then 2 weeks, then weekly, etc as blockchain bloat fully centralizes ETH.
They don't have the code to unstake yet. It doesn't exist and it's against their interest to create it.
So unless someone forces them to do it, they'll never do it. They'll just keep stalling and stalling and stalling until they say it's impossible. Good thing there's no such thing as Ethereum mining anymore. Otherwise someone would be able to pressure them to make the unstake upgrade.
Ethereum is the most successful scam of all time. Try to get your money out of it. Good luck.