Are you free to do what you want with an asset after you take a loan against it? Nop. You can’t sell it, in the case of bitcoin, you don’t even hold the keys to them.
Simply - the asset is no longer yours.
You will get it back after you buy it again.
The debt is raised using unsecured convertible notes. This gives max flexibility to MSTR and doesn’t restrict its ability to sell BTC if it needs to. If I were Saylor I would not touch the BTC and just convert the notes to equity if I’m not in a cashflow position to redeem.
