You obviously don't know what rikudou sage mode is. Here are a few facts about RSM.Regardless if they’re there or not, those 8 biju vestiges are functionless right now. He needs them for six paths senjutsu. Getting them to work(or getting them back) is the only thing preventing him from using six paths sage mode. The form isn’t lost, just not being used is all.
1. Naruto has sage mode kurama eyes however no orange pigmentation around eyes.
2. Naruto cannot touch gudodama without six paths chakra.
3. Naruto absolutely cannot fly without RSM.