The only means Sevilla will make an impact in the UEFA Champions League is to get new players that will complement the old players. The owner of the club Sevillistas de Nervion S.A should ensure they make funds available to Jose Luis Mendilibar to buy more players. The champions league will be more demanding than the Europe League.
The club had a bad La Liga experience last season finishing 12th. For them to be more active both in the Spanish league and the champion league they need more players. Coach Mendilibar would have to be more technical next season because he will have to compete with other top-class coaches. The club was just fortunate to win the game against Roma and they need to use this opportunity to make an impact.
Sevilla will certainly improve the quality of their team next season so they can compete well in La Liga and in European competitions. José Luis Mendilibar will probably demand the club and management give him a lot of budget to sign some good players he deserves after winning the Europa League title this season.
José Luis Mendilibar knows where his team's weaknesses were last season despite being able to win the title, so I think management should be able to help build Sevilla into a team that can compete in the top 4 of La Liga next season. Last season was bad for Sevilla because their performance was very erratic, but next season they should be able to recover.