The scandal broke in May 2022, QO's were extended/had to be accepted by the end of June.
The Senators extended the offer after they knew of the situation.
And I think the party that made the mistake was Formenton's agent. He made the bet that by December 1st, the players would be publicly cleared and/or this all would have blown over, and he'd then be able to get Formenton a multi-year raise from Ottawa or another team.
He bet wrong. Ottawa didn't offer a contract after the QO, and no other team had interest in trading for him. (Ottawa was reportedly just asking for a 2nd/3rd round draft pick in return)
If he had signed the QO, Formenton would be playing in the NHL just like all the other players from that junior team. Had he put up good numbers, he could have tried at a longer extension next summer. Now, he'll likely have to settle for a 1-year deal at a similar amount to the QO that was extended this summer.