I just called Greg. He answered me from inside the cone. He keeps his phone with him during his training times, not to answer calls, but to call for help if he needs to get out.
The way the cone is currently set up, outside assistants need to pull the pins to release the panel at the bottom, which he climbs down through.
Greg has complained about this repeatedly - it's an emergency hazard, for one thing, to be stuck in there! - but also just aggravating to him, to always be asking for help to get in and out of the cone. Management has promised him a solution to this at some point - some method for him to be able to at least release the bottom panel from the inside. But this may not happen for a while - they are still trying to handle more-pressing issues with the show, things that aren't working right, and this isn't as urgent.
So, for now, Greg keeps emergency-stage-manager numbers on speed dial, and the phone close by.