I’d love to help, but you’ve got too many “IF this fails, IF that fails” in your description.
It’s a fair requirement, but wouldn’t it be better to find a control system that is totally stable and works, with an excellent track record?
As for your requirement not to be locked into a single brand, I think that is a way to build in more issues.
My advice would be…
Research all the different protocols and choose just one that meets the vast majority (99.9%) of your “mission critical” requirements and stick to it.
Add different protocols where you absolutely have to, for anything Architectural or Non-essential, with openHAB2 translating between the protocols.
@ Everyone else…
See, I managed not to mention *****s at all