Okay, so, double post time. After numerous trial and error, it's been determined that yes, it does fuck with pathfinding. Lists my depot as inaccessible when i throw the switch. Another problem I'm running into is that my "drain" of sorts is constantly overflowing. Not much I can do about that, to be honest. I'm sure there's a workaround for it, since I'm having it drain directly back into the magma sea; you could probably drain it into Hell or a cave or some shit like that, but there are no caves on the map i used to test this and I'd get owned if i was digging into hell since I set up the first expedition explicitly for this project.
The best strategy to use for it would be to use pressure plates instead of having a lever be thrown, have them walk on the pressure plate the moment the elves pass the grates. The layout I used:
▓ = Wall
░ = unmined area
. = blank floor/ground
H = Constructed Floor
# = Grates
X = Door (so the dwarves can get in)
▒ and O's = Trade depot
* = open space
Ground level:
▓▓▓▓▓▓▓
▓O▒▒▒O▓▓▓▓▓▓▓▓▓▓
▓▒▒▒▒▒.#.........................................
X▒▒O▒▒.#.........................................
▓▒▒▒▒▒.#.........................................
▓O▒▒▒O▓▓▓▓▓▓▓▓▓▓
▓▓▓▓▓▓▓
Level above:
(this line is the wall one z-level down)
▓▓▓▓▓▓▓▓▓
HHHHHHH#▓
HHHHHHH#▓
HHHHHHH#▓
▓▓▓▓▓▓▓▓▓
(this line is the wall one z-level down)
Level below ground level:
░░░░░░░░░░░░░░░░░░░░░░░░░
░░░░░░░░░░░░░░░░░░░░░░░░░
░░░░░░▓*░░░░░░░░░░░░░░░░░
......▓*░░░░░░░░░░░░░░░░░
░░░░░░▓*░░░░░░░░░░░░░░░░░
░░░░░░░░░░░░░░░░░░░░░░░░░
░░░░░░░░░░░░░░░░░░░░░░░░░
On the level above ground, the magma came from the left, obviously. Had a pump stack bringing up magma from the 8th or so z-level down. Anyways, if I had maybe made that "drain" a little wider then it wouldn't have backed up... or if I had just drained it to a different place.
Either way, the pathing won't work if the fall is active, so you can use levers or pressure plates to activate it depending on your need.