That is why he should wait allowing Obito to think he is in control and lowering his guard down, Then striking suing all gathered full mental strength to seperate himself from Obito once they left Kamui dimenssion
Actually I see also another great reason for Kishi to leave Obito alive... at least until Madara vs Naruto and Sasuke battle ends. I think that Kishi will leave Obito alive so Black Zetsu will do his job and power up Madara while Kakashi being blind in Obito's eye return eye to Obito which somehow heals/retores light in bullshit way due to HASHIRAMA's DNA.
Naruto and Sasuke share a bit of their power with Obito so Obito will sends everyone alive in this battlefield to his Kamui dimenssion so Naruto and Sasuke can go all out and don't hold back worrying about hurting someone.
Kishi will stops nerfing/holding back Madara and unleashes his full power. The battle will be the most destructive battle in history with countires being blown up, maybe even continent and VERY UNLIKELY maybe even the planet will get damaged as whole.
Honestly I would like to see that so Naruto and Sasuke vs Madara would be the most epic battle showing INCREDIBLE DESTRUCTIVE CAPACITY