Indeed, this column reflected just last month on the anniversary of Keane's acrimonious departure from Old Trafford, when after one dispute too many, Ferguson decided that the time was right to part with the fiery Irishman.
However, there was a period when the once United boss needed the influential Keane more than he would probably care to confess.
As the 1999-2000 season got underway, captain Keane had entered the final year of his contract with the treble winners.
The talk was that Europe's elite were circling with the intention of signing the midfielder on a Bosman free transfer, just as Real Madrid had done with Steve McManaman from Liverpool earlier that summer.
Wary of such an approach, United offered their skipper fresh terms, which he duly rebuffed. Reflecting on those negotiations, Keane revealed: "I was a bit annoyed with the first offer put to me. Deep down they must have known it wasn't something I could sign. Our dealings have to be realistic. I am not naive enough to settle for anything less than a reasonable valuation of my worth."
Yet, just when it appeared that a move abroad was inevitable, the Premier League outfit caused somewhat of a surprise when they announced 15 years ago today that Keane had agreed a new four-year deal.
Although there was never any official confirmation, it was believed that Keane would pocket £52,000 a week, which made him the first England-based player to ever earn £50k plus.
Speaking at the time, Keane said: "I never wanted to leave Manchester United and the contract that I have now signed indicated to me United's desire to remain at the top of world football. It is a fantastic day for me, my family and the club."
Later that same day, the newly-committed Keane went about proving himself to be worth every penny when he scored the opening goal of the Champions League contest against Valencia, which ended in a 3-0 win to United.
He would go on to win three more Premier League titles and one FA Cup before he was sent packing, but Keane recently revealed to FourFourTwo magazine that he regrets not leaving United when he had the chance.
"My regret was that I should have gone abroad earlier in my career. I could have signed for Juventus or Bayern Munich. I had much better financial offers from them, but at the time I wanted to stay at United. I felt at home at Old Trafford," he claimed.
Even after he left United, Keane has never been too far away from controversy. In late November, he stepped down from his role as the assistant manager of Aston Villa, amid reports of a bust-up with senior players.