I don't think Arsenal will fail again this season with their young squad, because of the several failures Arsenal have experienced in previous seasons. Of course this has been a very valuable experience for Arsenal so maybe next season Arsenal will make better changes with their young players, but if Arsenal still fail again next season. This means that Arsenal must quickly find their mistakes so they don't fail repeatedly in every season.
In the last season, Arsenal had to play in Europa League and did not have chance to play in Champions League. In Europa League, they were beaten by Sporting Lisbon at their home stadium after penalty shootouts.
Arsenal will have their first season in Champions League after many years and it will be big test for their young players. With their performance in the past season, they can play well in Champions League but risk to fail is not small.
It will depend on their luckiness to fall in an easy or a tough group. Again they have big risk to fall in a tough group because they don't have good point recent seasons because they did not play in Champions League recent years. A new season will be a reboot for Arsenal to rebuild their position in Europe.