If we had a solid plan on how we want to play for now and the forthcoming two years. A strong conviction on what players we have and what we would need to have in order to play that formation/style etcetera I would be less hesitant to see Vidal go. Knowing that the money would be well spent. Like when Zidane was sold and contributed to the signings of Buffon, Thuram, Nedved etcetera. We then know sort of what where looking for and what we wanted out of it. Nedved turned out as AMC instead of the intended winger but we knew he filled a purpose.
As it is right now, I don't feel certain this is where we are, especially since Conte left. This is not a blast at Allegri but simply that he would need at least one year to figure things out to make those kinds of evaluations. Because of this I would prefer to keep Vidal another year and cash I'm next year when we have better idea of where we are, where we are headed and what we need to do/change. Of course due to my love for this guy I would love to keep him around forever and the team would benefit of having a few players around that has been around for a long period. Considering our team is ageing and the old crew that's been around this block for a long time won't be around for much long. We will need people who knows the club and can contribute lo stilo juve to future new players arriving. So there is that to consider as well.
Finally, I don't care how we play and what style. As long as we win I don't give f... Allegri can play whatever formation he wants but I share critiques that it seems like we've pushed it as far as we can and would improve if we had a backup plan 433, 343, 451, or whatever is something I don't care about, it's just numbers, but we could use having a more dynamic approach to throw at our opponents.