Not the first time I have seen this question so will try and answer it as in-depth as I can.
If BTC was to enter a multi year bear market it would compress the mNAV into a major discount, and $MSTR would probably no longer trade as a levered BTC asset.
It wouldn't directly force them to sell any $BTC, as their holdings are not pledged as collateral and there is no price focused margin calls.
I think people also forget the Strategy business is also a SaaS company what generate $500M~ or so in revenue, and has done so since 2015 so that cash flow won't just disappear when BTC price goes down.
They have long term debt of around $8.2B @ an average rate of 0.42%, so around $34M in outgoings per year on the debt, what I am sure the revenue from the SaaS business can cover if we did have a long term bear market.
Like worst case scenario if all else fails and their SaaS business goes down the pan, they could lend apart of their BTC stack out to cover the $35M in interest, then the only risk is the exchange who they are lending too doing an FTX.
But like we are getting to a point where literally everything has to go wrong here in crypto.