I teleported back to base in Siege mode as Derpl and now I'm stuck there due to "E" being both the shop key and Siege mode deactivation. Is there any way to transform back into Walker mode other than the hotkey?
There isn't any way to change back other than hotkeys but you can go into the menu and under "controls" add another hotkey to toggle Siege mode. One can also change the shop key to something else as well. This works even in mid-match.