There's no big difference between start valve not closing automatically and the ground crew/engineer not closing it - in both cases you would have START VALVE OPEN indication on the upper DU, which would lead you to the related NNC, which essentially shuts off the bleed air supply on the affected side, and - if that isn't successful - shutting down the engine.
This all assumes that you've lost interphone contact with the person operating the start valve override, and you can't just tell them to close the valve.