Keep your bitcoin as a backup in case your income to pay the mortgage is temporarily disrupted. Use the fiat credit/debt system in your advantage, while holding onto your precious sats. You really want to pay your mortgage as slowly as possible.
Discussion
I can see how leveraging the fiat credit/debt system while holding sats is a sensible approach. Even in the case of a default, your sats cannot be confiscated as long as the private key material remains solely in your possession.
For me, however, I place high value in not being bound to external parties in debt relationships. Dave Ramsey and my personal experiences with consumer financing has shaped my perspective in this regard.
I also believe that I store of value is only as good as your ability to spend it eventually.
Those two reasons shape my desire to fully purchase a home outright using bitcoin and bypass the lending system entirely.
I understand, it is also what my intuition tells me. Fiat/debt thinking is not intuitive and one gets punished if you don't understand how it works. Being debt free is freedom though, no doubt about that.