I think Arsenal can become better if Wanger leave....
As for goalkeeper, I think Cech's performance was ok in last season, However, he is about 30, which maybe too old for being a goalkeeper with stable performance. So Arsenal need to find another young player to make substitution for Cech, and that is important that the young player has to get more chance in playing match instead of just putting them on starting lineup. They need several years for training...