I'd have to guess the lowest would have to be either -9223372036854775808 or -2147483648 and highest being 2147483647 or 9223372036854775807. After you hit these points, my guess is you start falling up... lol.
Science will be done on this when I get a chance. Expect a new troll map with a terrible MS paint texture soon. I have to wonder what happens when you have a map thats 9223372036854775807 elmos high with -100 hardness and you decide to lob a nuke at it... does the engine merely crash or does it sink to the bottom because computers?
AN EVEN BETTER QUESTION: what happens when a pyro JUMPS on the map or if you have a roach cannon... do the units simply fall to hell because computers or what? Hahahaha... it'll probably be something boring but hey, its something to do! I'm already working on the texture map :D