Through all of this, we need to define SBC failure. A generic " the SBC system failed" is like saying "the engine failed" , there is a wide range of possible failure.

For it reaching the service limit and shutting off, I'd expect the MB SW _NOT_ to shut it down in flight and rather have it wait for the next key cycle. And remember, it gives plenty of warning, as in about 1/2 way to the limit.

Now, for the sudden failures , any small part of any system can fail at any time without warning. I'd hardly fault SBC for that.

Looking at the hydraulic diagram, the backup MC only operates the front brakes in the event of a total SBC electrical system failure. So yes, there will be a hard pedal and brakes only on the front.

If the pump or it's control circuity fails, there will still be a few powered stops left until the accumulator is empty.