If I consider the odds available right now then obviously Roma are still the big favorites to win but yes, even though Roma have a great coach like Mourinho. But for me personally at this moment Mourinho's job is still not easy, because Salzburg is also not a weak team that is easy to beat.
So with the aggregate advantage that Salzburg already has, then of course Salzburg will still be able to play well in the second leg later. With these factors, of course there is no guarantee for Roma to be able to beat Salzburg in the second leg later.
Regarding the game between Roma and Salzburg, I can say Salzburg is an unknown competitor for most of the teams and this team is not that weak at least I can say if they were weak they could be in the Europa league with other famous teams so this team can be a dangerous team even for a team Like Roma and from the 5 last games they played so far I can see unlike Roma Salzburg never lost a game against any team and just because if the last match Roma could beat Salzburg I can't say if they do the same thing again.
Certainly Salzburg is not a weak team. They have more than enough power to defeat Roma. We saw this in the first match and they won 1-0. Roma lagged behind Salzburg in all aspects in the match. The rematch will be played in Italy, but Salzburg has the advantage, it should not be forgotten. If they manage to retain the advantage, they can eliminate Roma.
Salzburg is probably going to focus mostly on their defense and keep a clean sheet for as long as possible. They have a good squad with a balanced game between offense and defense, but they also that they won't be dominating Roma in a home game. Roma is in quite good shape right now and they have a decent home game statistic so far. Salzburg can wait for their chances while driving Roma to desperation. It's very tough to say who will qualify for the next round. My guess still is that Roma will turn it around.