What if something like this happens:
1. Kuma arrives by crashing into Saturn and making him let go of Bonney
2. Kuma's near-dead state pushes Kizaru to finally turn against Saturn
3. Kuma, with his last bit of human instinct, starts taking away Luffy’s fatigue
4. Bonney explains things briefly to Luffy while in tears
5. Saturn defeats Kizaru quickly due to the latter's prior damage
6. Luffy gets up, G5 reactivated, and starts fighting Saturn