Warner has retired from Test and ODI but will continue to play T20 cricket, as per my knowledge. He is no doubt one of the greatest opening batsmen produced in the history that can play test, ODI and T20 format. He play test as genuine test player while in T20I he is a solid hitter like a young player. Aussies have a good domestic setup and they will produce some other great opener to replace Warner.
I was not aware that he has retired from the ODI format, he will now focus on league cricket. Since T20 is a short format retired players can play without any issue. MSD is still playing league cricket after he retired from all formats of cricket. Yes, he is undoubtedly one of the best opening batters that Australia has produced the good thing was that he was part of the World Cup winning team. He might be replaced by Marcus Harris that is what is being said by the Australian media.