So only 1 game series can exist. And everybody including you can only play this.  All other games go extinct and no new series are ever created.  Which would you chose?  

I'd probably pick battlefield because me and my friends play it the most.  GTA be my second choice. 

Zelda, too good to die.

Yeah, I'm not sure I would want to make that choice for everyone...

Kingdom Hearts. :D

Gotta go with Zelda, and it's a very selfish choice. To me it's the best video game series, one with the perfect combo of real-time action, exploration, and problem-solving.

Schoolmate. If it's the last game ever, may as well be fap worthy!

Final Fantasy would be a good candidate. Over thirty games, mostly RPGs, but that also cover most genres in certain entries or spin-offs, and there's a lot of room for social gaming as well.

Zelda.
But I'll miss Xenoblade and Metroid.

Rocket League. I could play this game forever (and always be shit )

You'd only have gotten a single player only game we every 5 years or so.  What would you do in between?