The manoevre has been called a loop, and for that we can calculate a safety gate. The final manoevre was more akin to a barel roll (p10-as the aircraft approached the vertical it began a LH roll). Maybe because the speed was lower that needed for a full loop, but no surprise that only 2700ft was achieved. The aircraft exited the manoevre 60deg off hdg, so perhaps AH accepted the lower altitude as he knew it was not a complete loop and intended to continue rolling, as he did and ended up rolling out off his planned track. Safety gates for barrel rolls are somewhat more fluid than loops.
He was flying a 'bent' loop with the change of axis on the way up. Now it doesn't really matter how he got there, but from wings level and inverted he had several options. Yes he could fly the second half of a barrel roll, but that would have kept him pointing away from the display line (effectively behind him). It would have avoided the accident, but was never going to work from a display point of view which is all he appeared to be trying to focus on. I agree that a BR has a very different kind of gate parameters, but last thing you'd ever want to do from an inverted but 'low' height is to pull through. The second half of a loop is always going to use up more sky than any other course of action.
Think of it another way, if your barrel roll goes awry, the last thing you'd want to do is try to half-loop out of it!