Of course it could also indeed mean that you can continue playing even if Geralt has died at the end of the game. But that would imo be the most horrible possilibity. That'd be just downright stupid game design.
Other games did this too, after the main protagonist died in the end, you could still do some of the side quests that you didn't have time or couldn't finish, and it didn't really feel weird at all. I mean if you play the game, and you can't finish a side quest, because you don't know how to proceed (like me in W2 with "The runes of power" mission when I first played it), you might decide to move on, and maybe later you want to try again, what do you do? Either reload the savegame, and then do the story missions again if you want to have all missions completed in the game, or do another playthrough of the whole game and do it then. Hmm.. that actually sounds good lol. But yeah, after finishing the game I would like to be able to run around, finish whatever side missions I couldn't do, I missed this from W2, not even because of the side quests, just to explore.