Once again I did something crazy: I noticed that the tundra continent was almost full, so I opened 2 pwa on different email addresses, I started creating a character on both, with the first I clicked on the green button to validate that I will start in tundra, with the other one I stayed at the screen that ask in which region I wanna start. And then with a 3rd email address, I checked when the new continent was open, and once it happened, I wanted to create those 2 heroes to see what would happen:
For the second one, I'd like you to confirm, but it seems like you actually though about the case of someone starting to create a hero a few seconds before the continent was full, because it really seems like the only choice "northern tundra" was changed to "northern grassland" without me doing anything, I'm very impressed. For the first account, I just started the hero and it was in grassland, so, even though it's extremely unlikely (to the point that you should probably do nothing about it), someone actually can start creating a new hero, validate that he will start in a specific continent, and by the time he validates the next page (like taking a few minutes thinking about what artifacts to keep), the continent can be full and he will be surprised to spawn in a different climate. If you REALLY want to fix that, I would recommend simply putting the continent "choice" page last.
If the continent does change a few seconds before validating, you can add a warning about it so even if it happens last second and cannot be humanly avoided, someone that really doesn't want to play in a specific continent will be able to cancel everything.