Margin calls don't really exist as far as loans are concerned. Once you have agreed collateral, and an agreed schedule of payment, you only get in trouble if you miss a payment, regardless of how the collateral fluctuates in value.
It is doubtful Z has any margin call issues as he has so much stock, I can't imagine he would have pledged even 5% of it for loans, so he can just hand them another chunk without even blinking (which he generally doesn't do any way)
This scenario would just be basically impossible.
Separately, my bank tried to sell me a "Pledged Asset Line of Credit" that would also have required the collateral to maintain a certain value or there would be forced liquidations.
Can you link an example of a bank or similar that lets you borrow against stock or options collateral without margin call risk?
The original post you were replying to talked about founders borrowing against their company's shares as individuals, not companies.
> it is unlikely that a lending institution will accept shares as collateral due to the wrong way risk
That's my point: Nobody's getting a special financing deal on their company stock as individuals to eliminate their margin call risk.
Multi-billion dollar hedge funds get a personal contact at the bank, but even they will get margin-called borrowing against stocks as collateral if it goes against them.