So Ciri has been rescued from the Isle of Mists, Kaer Morhen defended with Visimir killed. after a brief visit to Novigrad to get Gels and round up the sorceresses. I've just visited Emhyr and killed Mad Man Lugos with the Druid dude and am off to find the Sunstone. Is there much story left after I've found the sunstone and summoned Eredin? It seems that that should be the final confrontation if all goes to plan.

So I'm wondering how much time I have left with this awesome game (I know I can continue after the main story is over but usually I lose interest when I beat a game's main story, plus I still have to finish GTA5).

I'd say an hour or two at most left in the main story. The final confrontation is amazing! I really enjoyed my (super) long time with this game and look forward to the DLC

After fighting Eredin, there is one more playable sequence. Depending on certain choices you've made, it will be one of three different sequences