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.