Can I still be respawned if I die by falling off the map?
From personal experience, yes you can be respawned if you die from falling off the map. I accidentally ran off the side when trying to dodge a grenade inside a smoke bomb, and my box spawned on the map, near the edge and my teammates were able to grab my banner and respawn me. I have also recovered several of my teammates banners and respawned them after they jumped off the edge.
If someone managed to push your box off the edge after it spawned near the edge, I am unsure of how that would be handled. It may respawn back in bounds, or it may be gone forever.