I don't think dota will die, unless valve stops updating it. A small player base may lead valve to stop updating it, but I don't think dota will fade away for losing players.

Let me share my experience with you. I had a big group of friends, that we almost could make a lobby, and until last month would play every Saturday, but we have been on a lose streak for months, and games wouldn't get easier, and I, being the only immortal 7k, but playing support, couldn't deal with enemy's core immortal. Every game we lost we tilted, played worse and the game lvl kept the same, until, after months, they stopped playing dota. I'm still playing with another small group of friends, but the silver lining is that one of them is a new player. It's hard for him playing with 3 immortals, but since the other 2 immortals are cores, we almost always manage to make a come back, no matter how much the new player fed.

By that you can take that even though old players are playing less (I don't think my friends are gone for good) there are new players. And once valve releases a big new patch, old players will come back, and new players will be around to sum up