An 80%+ drawdown and margin calls would mean assets must be sold to meet the call and MSTR would be shaken out of their BTC holdings. That would materially impact the stock price by a balance sheet impairment both directly from a BTC fall and having to sell other assets to meet the margin call.

Saylor is far more intelligent than I am, so maybe he has it covered, but I've seen legions of so-called geniuses wiped out in the markets by overextending debt in the face of volatility.