As in all diving where you cannot make a direct ascent special precautions have to be taken. Pony bottle is just one of them. Real cave divers have at least two independent regulators, two lamps, lots of extra gas etc etc. And still a number of divers diving in caves die each year.
A good friend of mine owns the local dive shop and has been diving since the early 1980’s or earlier. He is probably one of the best divers in the world. He certified to train every certification PADI has to offer including cave and Wreck diving. Which is basicly the same thing. He told me when you cave dive you take two of everything. When you enter a cave or wreck you use 1/3 of you air going in and have 2/3’s to get out with.