Its been done before. You spec into high intellect and use bad juju to get your super as a sunsinger. You kill yourself right when he teleports and revive. Idk saw a video of a guy doing it.
It's impossible to solo Atheon while going through the boss fights mechanics. However people have found ways to avoid the time warp. Such as a warlock using self res and a titan sitting in a place out of the teleport zone. This requires pure dps w/o times vengenace though so its pretty difficult.
Warlock jumps off the map when Atheon opens the time stream, then uses radiance to self res.
Hunters can jump out of the map so they won't be teleported and snipe Atheon from there until he's dead.
Don't get mad dude, go to YouTube if you don't believe me. It will take you about ten seconds to find the videos.
It is only closed if the place has not loaded as a Darkness Zone. If it has the door is open. If not, then you can leave and come back in.
The only part you can't solo is the gatekeepers.
I have had the checkpoint before and gone through it solo so I could get people for Gatekeepers rather than some littles shits who would take the exotic chest and leave. I definitely does open for a singular person.
Did I say anything about the gorgons? No, because I don't believe you did either in your post. You stated Atheon couldn't be solo'd and I pointed out that that was incorrect.
Hahaha, I mean all I did was point out it was possible. I didn't expect him to get all butt hurt about it, especially considering it would take ten seconds to type "Atheon Solo" on YouTube and find about 100 videos of it being done.