If I’m playing warlock whose goal is to break his fiendish pact what happens if he does?

Whoops, also @mikemearls. I'm sure you guys have answered this a million times. Is it DM's discretion?

— Zack Loran Clark (@zackloranclark) September 6, 2017

DM's discretion. I play it that power once given can't be taken back

— Mike Mearls (@mikemearls) September 6, 2017