Half hour sitcoms and dramas didn't kill film so I highly doubt simple mobile titles will kill their more involved and complex console brethren.
That's one threat. The console market consisted of a diverse set of gamers, from hardware shooter fans to casual coop players and families and kids and whatnot. 10 years ago, if an eight year old wanted to waste an hour, they'd fire up their PS2 and play something, Crash Bandicoot or something. Now an eight year old can find that time-killing activity in a mobile.
"But the games aren't there!" No, but they could be, and there's reason to think they might be. There are FPSes on there, for example.
"But the controls suck." Yes, but 1) new games can factor in the controls and provide a console experience that works with them. 2) All these devices now support controllers and TV connectivity. If I want to play Dungeon Defenders 2, I can use a tablet connected to a TV without needing a console. Dungeon Defenders was released on PS360 - you needed a console to play it (or PC). DD2 is releasing on tablets as well. You won't need a console to play this arcade game. Things are definitely changing even if slowly. In fact, DD2 is scheduled for iOS and Android but not XB1 at the moment, so XB1 owners wanting to play this will do so on a non-console (unless they have PS4 too, natch)
Then on the other side, we had others reason to play console. PC was overpriced and complicated - that's no longer true. All its games were KB+M, but now controllers are widely supported. It's not as simple as console yet, but it's not the nightmare it was. The price of entry isn't as good value yet either, but the performance is going to be way more. We even have cheapo tablets offering full Windows, so you can have portability with your software library on tablet as well as your home gaming machine. Then there's the library and the fact PC now wallops consoles in many areas because it's completely open and devs don't need to jump through as many hoops nor put as much cash up front to get released on PC as console. And PC's on TV just works now. Then there's the fact consoles have become more buggy and patch-tastic, robbing the platform of some of its advantage.
Then, on another side, you have game streaming which offers a convenience. For Joe Gamer who doesn't particularly notice lag, streaming might be the choice.
Consoles used to stand apart, offering something unique that no-one could compete with. That is no longer true, and with so many different alternatives appealing to different demographics who used to only have consoles as a choice, it would be pretty amazing if there aren't any losses from consoles. The only counter to that is the potential for far more people gaming in general, so the losses from some demographics are made up for by new blood.