What happens if you get promoted or relegated will totally depend on the 'numbers game' that got you in the higher league level. So who knows. With the numbers of teams in leagues so fixed it'll probably be happening somewhere to somebody at most levels but its expected more at higher levels. Servers with a lower high level population will be more susceptible too.

I'd expect that competition draws are built from the top down. The bots are added/deleted towards the bottom.

Personally, I think it would be a good idea if higher level teams were clustered into their own servers to manage that population better (if technically possible). That would make it easier to then consider 'bot filling' the levels below.