In the second leg, Dortmund must try harder to get a win in the deciding match. A draw is not good enough, but looking at the performance of both teams, it is considered fair and quite satisfying for both teams. But in the second leg, of course, everything will be different, Dortmund might be able to get a win with their full effort. I hope to see a really all-out match from both teams in the second leg.
If you look at the appearance of both in their respective Leagues, it is not much different so it is still quite difficult to predict the course of the match in the second leg. Lille is more advantaged by the draw obtained when playing in the first leg so that the game in the second leg will take place at home. In terms of pressure, Dortmund may be much greater, but anything can still happen. Hard work will determine the results and if the coach has a better strategy then one of them still has a good chance of winning, although Lille itself is much more advantaged playing in front of their own audience.
Lille is doing a lot better on their own league, they are fifth and have a chance to finish fourth and go to UCL again, if not then at least they could go to Europa league, they have that chance and not doing that bad. Dortmund is doing terrible though, it's most likely that we are not going to see Dortmund in any of the European competitions next season, they are going to finish the season out of UEFA competition rankings and they are going to have a season of just being in Bundesliga.
This doesn't mean that Dortmund should lose of course, it just means that you can't look at the leagues and make a decision based on that, it is not the same league, and it is not the same teams in each competition they are in neither.