If you believe Allegri can provide good results for Juventus, then this season Allegri should succeed in making Juventus dominate Serie A. Because after all, this season Juventus clearly only played in Serie A but in fact? Juventus even continued to decline and I don't think it's worth it for Juventus to keep Allegri. Try not to attribute success to the past, because to be a great coach ofcourse the coach will be able to maintain goodperformance and quality for the team itself. But, if you really like Allegri to stay at Juventus, I would say congratulations, because then Juventus will never be able to win trophies again.
From what was available to Alegre he achieved the maximum result, he returned Juventus to a good defense, but he did not receive any funding to strengthen the attack, and is now forced to play with Chiesa in attack, a player who is a midfielder, albeit an attacking type, but no hard to understand that Alegre is doing this simply out of necessity. Of course, Juventus should have kept Alegre in the team, but if they think they can find something better, then let them try, I think after this Juventus will slide back down again.