It's difficult to fight in the Champions League when a team doesn't have high-quality players, but in the season that just finished Sevilla were still able to stay in the middle area of the final standings and it's not that close to relegation. But for next season Sevilla will have to fight even harder because they are already in a tougher competition apart from La Liga, because the Champions League is a league for the best teams from several domestic leagues.
Sevilla are not the favorite in the Champions League, but they are the better team in the Europa League. Instead of hoping for the Champions League title, I think Sevilla should focus on the Europa League and win another title next season.
It might be good for Sevilla if they can compete with the top teams in the Champions League but even if they do qualify for the round of 16 I believe they will only fall short before reaching the quarter-finals. So even though Sevilla failed to qualify for the round of 16, they have a better chance in the Europa League.
Champions league and European league are very different tournaments. I'm sure the teams will hold up against their star-studded roster, but I'm not sure if they can make it through the group stage. If they finish third in the tournament, they can be favorites again in the European league.