If Atalanta lose the next two matches and Roma wins the next two matches then Atalanta and Roma will be equal in points. However, even though the points are equal, the Roma team is behind in goal difference. So I don't think it will be possible for Roma to qualify for the Champions League. Atalanta will be able to keep the fifth place in the table.
No chance that Roma will catch Atalanta. Atalanta must win against Torino, it is a home match for Atalanta. Even if Atalanta will lose points against Fiorentina, they can get points in the match against Atalanta. It is enough to secure their position in UCL zone. Roma should be satisfied to finish in Europa league zone, they will have an international match for the next season. Roma must play better in the next season if they want to finish the season in UCL zone.
Roma team has performed very badly in the last three matches. This is why the party has fallen behind. Especially after the defeat in the match against Atalanta, the Roma team has fallen further behind. If Roma could win against Atalanta, Roma would still have a chance of qualifying for the Champions League. And at the moment Atalanta and Roma would have been equal on points.
Yes, Roma performed quite badly toward the end of the season. There is a decrease of the performance of Roma player. I am not sure if it is caused by they failed in Europa league. But this shouldn't happen, AS Roma must focus on the remaining matches.