I usually requeue or try calling a vote if theres only one of them. It's impossible to counter them otherwise and if you waste time by trying to kill them instead you'd still be losing as they don't lose anything from dying. Valve will never be able to do anything about them, cheating will always persist in any game, however they could've introduced a lot of things that could hinder their ability to cheat, but right now TF2 is practically on hold pretty much fully, so don't expect that. Sadly, it is what it is.