I think you have not understood it well and I have already explained it in the thread but I think it is easy to get lost in such a long thread, so I will explain it again: the debt that MSTR has is unsecured, therefore there is no collateral backing it.
As of today MSTR finances bitcoin purchases in two ways:
1) ATM: it sells shares and with the money it buys bitcoin. These are newly created shares.
2) Convertible debt. The interest paid is ridiculous, 0% or close to 0%, and two things can happen, the share price can go up, so the convertible debt is converted into shares, or it can go down or stay more or less the same, so MSTR has to repay the debt, which is not much of a problem because the debt to equity ratio is quite low.
Nope. There is no liquidation because there is no secured debt. No margin calls.
Something similar to what he did in the previous -80% crash?
If Saylor has been so successful, it is precisely because he does not think like you. I know it is hard to understand, but that is precisely the basis of success.