One scenario he mentioned is having a brake failure while taxiing in a congested area.
I was taught
"Never point the aircraft at anything such that you will hit it if the brakes fail."
So my answer would be "carry on steering on my planned path, which by design isn't going to collide with anything, at an appropriate point turn the engine off, and in due course the aircraft will stop, obviously without hitting anything".
This means that if your planned clear path involves corners you should not, ever, be taxiing so fast that you will actually need the brake in order to get round the corner. For your PPL test you're unlikely to be driving anything so powerful, and we hope you're not driving anything so badly adjusted, that you'll be accelerating with the engine idling, so you won't need the brakes to keep going at a safe speed in a straight line.
Worst possible result: your aircraft is stopped somewhere inconvenient that holds up other people. But in that case they might help you push it!