Actually no. ALL of Strategy's BTC is unencumbered. There cannot be a margin call on it.. But seems like there are talks about Micro Strategy (MSTR) accumulation-risk, forcing them to suffer a margin-call in case price goes under certain amount.
As far as accumulation risk: I think "plebs" have bought as much as they can. Only 0.1% of the population is capable of comprehending bitcoin. 99.9% of people will not be self sovereign bitcoiners, nor will it matter much to them.
Companies, Institutions, Banks, and Nation states will buy the remaining bitcoin, NOT individuals....the supply of individuals capable of understanding it has been exhausted.
Just as most people think of their fiat derivative fractional reserve rehypothecated federal reserve notes as "money", they will be completely unaware of the bitcoin backed money that takes over. I believe it will be a volatility stripped derivative of bitcoin like Strategy's STRC. Not forever, but during the transition period from a fiat standard to a bitcoin standard.