It's all really going to depend on the price. This will determine WHO is mining not if we can still mine. Nothing more, nothing less.
If the price is high enough then big mining farms will continue to dominate. Make no mistake about it. If having 1 miner makes you $1 a day then having 1,000,000 miners will make you $1,000,000 a day so if you have the money you buy as many as you can.

If you cannot make money then the larger miners are going to go away and mining will come back to the home.
If I loose $1 a day but I enjoy mining bitcoin then guess what I am going to keep mining it with something sitting in the back room [So long as I can run it on 110v and it's quiet]

So, it's not "For how long can we actually mine ?" it's how long can big miners keep mining. For people mining as a hobby or for fun, making or loosing money is a secondary consideration.

Just my view.

-Dave