Well written post unfortunately I don't know the answer, I am under the impression that bsg is fully open source, so I suppose technically if @Blockstream were to fully cease operations and the app was unavailable, then one could spin up a DIY version?

I have thought about using a bsg wallet with a jade in addition, and the option for disaster recovery to a 'rival' wallet has crossed my mind, I haven't taken the time to check bsg's derivation paths etc, to see if they differ from standard bip39.

Darth may have written a guide on this, so it's worth checking his list.