> below miner leaving rates.

What does this mean, sorry?

> the edge case collapse the entire system.

If you mean that if it reaches a certain point, the entire system will collapse, it means you don't understand the difficulty adjustment. If it's too expensive to mine, then some miners leave, which makes blocktimes be longer, but not to worry because the consequence of that it just that difficulty will go down, which means that you need less hashrate to mine (and maybe some of those miners that leave will come back because it is profitable again for them). This means that it is essentially impossible for all miners to leave at the same time; some of them stay even if at a loss, and some of them are just hobbyists that can already feed their miners with solar power (so there's really no loss for them in leaving them connected).