There was no deal. It's not a deal unless it is in writing. The whole process the NFL has set up that only allows to hire another team's coach until after their season ends makes no sense. Why can't they let them sign an actual binding contract after the conference championship games? I don't see the harm with that.
But there was nothing preventing Irsay from continuing to interview candidates while Josh was still in the playoffs and not under contract with Indy. Nothing.
He might have interviewed Vrabel, been impressed, not have any reservations about moving his family and immediately give him the contract instead.