City do have the option to match any bid which would give them first refusal, but Sancho may not want to back there. From my understanding, Sancho couldn't wait to get out of City and was ready to join United before City put a end to that.First, this would be a dispicable try. Everyone in the world of football critised Barcelona for thatone (and their move was based on their own stupidness to let Neymar suprisingly go and not planning in the longterm). Second Watzke claimed after that case, that we will not tolerate any actions like this anymore, and given the contract situation, he would let Sancho sit in the stands. Third point: Your try wouldnt remove the clause City has got, so even if you offer huge amounts of money, City has all the oportnunities to offer more and would always be the first choice. To say the last: Sancho extended his contract in the begining of the season to 2022, i can only repeat myself on that one.
We are a club you can work with and are always honest in buisness and to our players, our image in developing youth and run a Club well is as good as us as an buisness partner. If you try something like you mentioned, it will hurt you and the buisness as a whole, if you know what i mean (Sorry for my bad English).
I personally don't think Sancho will want to go back to City, especially with the way he left with a cloud hanging over both player and club.