Normally he wouldn't be even able to descend there as vertical caves require massive amounts of rope, but Veryovkina is so huge it was rigged permanently β descent to the bottom takes three days and there are four camps on the way with basic supplies.
This is how he was able to descend to camp at -600 m, spent a week there (!) and then decided to o further. At -1100 m the cave however becomes much more technical, which was where he got stuck and died.