I still play Smash Wii U all the time, and all the DLC kept on giving me something to go back to, so definitely.

I've had many games that I played for over a year. I remember playing Halo 2 up until the release of Halo 3. I remember playing Ninja Gaiden 2 well after 3 came out. Most recently Destiny and GTA V have made the list. Although in the case of GTA V I stopped playing it for over a year and then went back to it. Now I'm hooked on the game all over again.

WoW for 7 years counts?

It all depends on the game

I like to stick with a few games and play them for a while so I can play a game for over a year even without DLC
but things like Splatoon updates did make the game feel fresh with each new update so that was really neat

I'm still playing RL. Though it's not the DLCs that make me continue to play but the free updates.

depends if you plan to purchase DLC in the first place. Buying a new game is a lot of times cheaper