Even if Atalanta loses the remaining games, and Roma wins and they are equal on points (now there are 6 points between them and not 5), then Atalanta will still be in 5th place because according to the Serie A regulations, in case of equality of points, the number of points scored is first taken into account In personal meetings, Atalanta is ahead by this indicator (1 win, 1 draw).
As for getting into the Champions League, this is in any case more profitable than being in the Europa League - there you will get more money than even if you go very far in the Europa League.
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.
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Nope. The goal difference in case of equality of points matters only in the third place. In first place is the number of points scored in personal meetings, in second place is the goal difference in personal meetings.
Thus, even if Roma makes +20 in the last games, and Atalanta loses two games with a score of 0-10 and gets -20 in total, there will be equality of points, but Atalanta will still remain in 5th place.