The Witcher 3 is a big game with lots to do and up to 200 hours of gameplay across its main and side quests and the huge number of tertiary stuff which you can get up to.
But you may have been worrying about what happens when you've done so many things that you can't level up your character anymore. It turns out, that's not a thing you ever even have to consider as Geralt has no hard level cap.
So you can just keep on playing the game until you have unlocked every single one of the dozens of abilities to their highest point. And then keep on going.
Of course, at that point there are no upgrades left so it might start to feel a bit fruitless and you'll likely be long finished with the story missions and mopped up every last question mark on the maps. But it does give players total freedom to play the game exactly how they want - you can just kill random mosters for hundreds of hours without ever touching the story and you'll still get rewarded, though the tiny amounts of XP might make you go insane after awhile.
There have now been calls for a New Game Plus mode which would allow you to retain your level progress but start the story over again with all of these skills unlocked and more difficult enemies. It's a step which seems like a no brainer for CD Project RED so hopefully it will happen soon. It's also likely that the upcoming expansion packs, due in October 2015 and early 2016, will add new abilities and give the game even more longevity.
More as we get it.