Gasperini wasn't fired, he left the club for Roma after nine good years with Atalanta. He built the team to thos standard, he could have waited for two more seaaons to perfect the team performance in order for them to win Scudetto. I don't think that Atalanta will be able to catch up fast with Juric game pattern fast and that will affect their performance in the beginning of next season.
The influence on Atalanta's performance change at the start of next season could happen because Juric's coaching style with Gasperini is very different because Juric also has his own way of training all the players at Atalanta. I just hope Atalanta doesn't become a weak team just because their old coach left because if Atalanta becomes weak just because of that, of course the one who will suffer the most shame is the new coach, Juric. So for next season Juric will have a difficult challenge at Atalanta because he needs to maintain Atalanta's best performance and appearance even though it might not be as good as last season.
It is normal for the team's performance to decline relatively after a coach change. You have to see how well the coach is doing in the long term and how much he is working for the team. He must be given time to prove himself. He has some plans of his own and there are experiments. He will need at least 10 matches to complete them. If he cannot improve even then, then it is definitely his failure. Atalanta's poor performance is expected at the beginning of the upcoming season. But we will have to wait and see how they do.