My first post, hi all- skip to the last 3 lines if you want the short version.
I was very unfortunate yesterday. Running a genuine cuav pixhack 2.84 on am s1000 octa which has been stable with 3.5.2 fw, it suddenly had a spinning horizon and bad baro health on the morning of my assessment. I’d updated fw on another copter the previous evening and changed Params and couldn’t remember doing anything to the s1000- checking Google similar problems indicated rolling back fw fixed the issue so I reinstalled one at a time back to 3.4.6 at which point the problem appeared to go away. At this point I didn’t realise the problem hadn’t gone away- the warning had! I’ve now learnt how to check press abs in mission planner. Needless to say in GPS flight modes the copter climbed uncontrollably and I did the assessment in stabilize- failing on a technical failure because I couldn’t demonstrate RTL failsafe, we were at an airfield with permission to fly to 100ft and within 10 seconds of hitting RTL I was well past that 
Is this correct behaviour and is this what 3.5 would do if the baro failed mid Flight (admittedly it was telling me not to arm because mine was already dead)?
I’ve resoldered the tiny tabs as best I can of the baro on the pixhack after troubleshooting it down to the hardware and it now works- but I don’t want to trust it. The fc only has one baro as do lots of others I have.
I know apm will switch to a second baro if present, but does 3.5 use GPS if the baro reports bad health in flight or will bad baro health result in a death climb?
Thanks