if you could only play one game for the rest of your life, which would it be

Well that's very limited, anything that you will play for the rest of your life you are going just to get bored after a time, but in this case, i would prefer League Of Legends, i know it sounds crazy in the first place, but you will get these kind of crazy updates of new champions so yea i believe you have something new to try time by time XD