You do raise a valid point that as long as there is a copy of the source code somewhere, Linux will still be around. I am sure that it will be around forever just because of that reason.
But what the bigger deal is here is that if Linux somehow gets driven out of the current edge-of-mainstream back into the "hacker and CS-major OS" niche is that we'll see development for it slow greatly. We'll see no more new 3rd-party applications or the necessary-evil stuff like binary blob GPU drivers and Flash plugins. I don't know about you, but I am glad that Linux is gaining popularity because the 3rd-party development makes it much more usable and a real choice for general use.