When the event ends, can anyone then just walk through to East Solstice if they've had no involvement in the event? I assume the whole zone then opens up normally to everyone.

I play on PS/NA during north american mornings.
Even at this non-prime time, usually after a new area becomes available, the quests are crowded. The area around the quest givers for incursions and delves is busy. And all the WBs and incursions are crowded and go down fast. This is true for at least the first week or three.

Eastern Solstice has been open for 4-5 days on this server. I'm questing in there, doing both the main and side quests. I'm the only one there most of the time. At most, there's 1 more player.
When checking the quest givers, there's maybe 1 other person there. There's no one at any of the world bosses, either on Western or Eastern Solstice. If I ask for help, I maybe get 1 or 2 other people to help. I drop any Ghishzor WB quest, because I can't solo him and no one else will go close to him.

I know part of this is due to the fact that the quests are split across Eastern and Western Solstice, and people who did all of the dailies for Western might not know they now include Eastern Solstice. And a few people here have said they're not questing in Eastern solstice until they know the bugs are fixed.

But even still. This is the first time I've really felt the decrease in player base, given when I play, since I rarely play during prime time.

I only say this as a data point, ZoS. I do most of the game solo anyway, esp questing, so I don't mind. I have most of the furnishing plans that drop from dailies, and will buy the rest, so I'm not terribly bothered. But.

There's no one here.