Unfortunately there's not much that could be done about this and I feel your pain. Buffing demo health wouldn't be an option due to maps with long prefires or pipetricks becoming easier, and I would say that disabling fall damage could fix this for some situations. However, sometimes you die without any fall damage like with an uncrouched double or water double. I don't really know much about the workings of the game itself around these deaths other than the basics but maybe someone could find out a solution .