From whom should they run if Kizaru and Saturn are defeated?? Cannot compare to Big Mom where Luffy barely defeated Katakuri and was out of fighting, and they then had to escape from many strong fighters like other Commanders or Big Mom herself!
Unless you are saying Luffy will go down and unable to continue fighting himself, the narrative of escaping would be gone if he defeats Kizaru. Apart of there not even being the time to waste on fighting an Admiral anyways. Even if you claim he takes him down, he would surely need his time to do that.