And if Sir Alex Ferguson had decided to replace his own batteries and hang around for another season or two, that scenario would have come to fruition.
But David Moyes came in from Rooney's spiritual home of Everton and gave him all the love (and money) that he needed.
The England star remains a Red Devil.
It is not a wild observation to make that if United had not had Rooney this season that their Premier League position could be a lot worse.
The team's performances have ranged from average to shockingly poor.
Indeed Moyes himself said of his team this week, per BBC Sport:
Our form and our performances have not been consistent enough. We have shown some really top performances and some really low performances. We have to get better at that, but it is going to take time. We are not going to be able to do everything immediately.
Thoughts are already turning towards next season with a fresh approach and new players.
But one man who will still definitely be in the side is Wayne Rooney.
After signing his last huge contract with the club—and a train of thought that says he will take over the club captaincy once Nemanja Vidic vacates the honour in just a few months time—Rooney's place at United has been solidified.
It is difficult to believe that it was only a year ago that he was being dropped for Sir Alex Ferguson's last game in charge at Old Trafford.
So what is Rooney's value and worth to United in 2014?
His stats tell some of the story:
In the Premier League and Europe this season, the player has 13 goals and 14 assists from 31 games, per WhoScored.com.
Rooney has played in his favoured No. 10 role this season, which might explain his lack of goals but it also explains his excellent assist rate.
Even with the general lack of a sidelined Robin van Persie in front of Rooney, he has still managed to create positively for others.
When you take into account Rooney's form this year, consider his previous achievements and his consistency in the last third, he is still very much one of the best forwards in world football, and his price-tag would reflect this.
However, Rooney does have one large technical weakness.
His first touch has never been extraordinary. As a player, he has always been busy and on the move. He has never displayed the first touch of a world-class player.
Consider the control that Paul Scholes would have on the ball. You can even look within the United squad today and see that Rooney's first touch is not as good as Juan Mata's or Shinji Kagawa's.
But Rooney has an x factor that most do not and a work-rate that singles him out to a certain type of supporter.
In the current market, Rooney would be worth close to the £40 million mark but no more than that.
His ability to sell shirts and his position as "England's boy wonder" does give him some added value, but at 28 years old, he is at his peak, and the road only goes south from here.
The next 12 months will be interesting, observing Rooney as the alpha-male at Manchester United once again.
Can Captain Rooney lead from the front and drag his club up by the collar in a Bryan Robson fashion?
Will he skipper like Roy Keane, all blood and thunder and public dressing-downs on the pitch?
Or will he put his comfy slippers on and see the rest of his days out in Cheshire, a very very rich man, at a club in spiralling decline?
Will the fire still be there inside of him?
Only time will tell, but Rooney has to prove himself all over again, as does every United player after this season.
They all need to show that they have a value to Moyes and have the best interests of Manchester United in their hearts.
Rooney will set the example. Let us hope that it is a good one.