Personally, I don't think that an /unflip command is really needed, simply because when you flip you can just teleport to a service and that creates a bit of more realism. Also the only one I believe this can happen is if the unflip commands teleports your truck to the same location so it can actually unflip it, which may cause a collision with another vehicle nearby, which will make the situation worse. I do understand that some people really have issues with spawning in highly populated areas, but I don't think that such command will be possible to be made.