If Mignolet has said this game represents a chance to save this season then I agree with him 100%. Lose this and we will have lost 2 cup finals and had a poor league campaign making it a disappointment overall. Win and we have another European trophy which makes it brilliant with the added bonus of champions league football next season. What is wrong with him thinking it makes the season ?
I have no issue with his quote. It's true. If we win the tournament we will have had a great cup run and secured champions league football. The league season was poor but objectively speaking, the season would have been saved. If we lose, we will have come 8th in the league and have no success to speak of, barring a few great memories from some great games (which were ultimately in vain) - not a good season.
Mignolet is complete right. Winning the cup saves the season.
The only potential problem is that he has the "fear of failure" mentality rather than "chance of success" mentality. But really, what does it matter? You can't change the way you think overnight.
Much more important things to think about than massively over-analysing a quote.