I'm not sure you'd be allowed to leave LHR on ETD's just to come back there( admittedly transiting). Horrible situation to find yourself in at least you are safe personally.

Regarding your TP's being short I think this is a very good case for BA showing leniency as they can see you had the points covered and it clearly wasn't your own fault. Idk if they'd require you to make up those points in a fairly unique situation but confident that somebody on here could probably point you in a good direction to have that chat when you're home safe.

Update: They are super cute and nice to find some brevity in what must've been a horrible situation. I'm sure not even BA would be so mean to refuse to honour the Gold irrelevant of any published rules. You can demonstrate that you would've had the points needed if something totally out of your control hadn't of happened