What would you do if one piece ended.....

It's the same as Naruto it will, if Naruto ends everything will.

theres still 10+ years left till that happens

Then you deal. Just like fans of Naruto or Bleach or whatever else. In my opinion . . . You vocally protest as you watch it you the bitter end if that's what happens.

Havent watched it

I'd go on living my life as normal.

i will be SAD............!!!!!!!!!