Getting to the orbit was a frivolous exercise in the first place. The castaways had no need to get into space, other than to get out of the reach of the cavemen - and that would have been far better achieved by camping out and slaying any approaching giants. Leave it to Kirk to effect the actual extraction, as he's so much better equipped to achieve it.
Sure, Kirk could have come back and extracted the seven corpses.
That the creatures were able to kill two men armed with phasers proves staying put was not the right decision. Latimer didn't see or hear them coming, so the natives can apparently be stealthy when necessary.
Gitano had his phaser knocked from his hand and without it was helpless to save himself. The creatures have good aim. They pinned Spock with the rubber boulder very neatly. They can disarm and trap their fleeing prey.
The planet was full of these creatures, according to Kelowitz. Even with phasers, the landing party might not have been able to mow them all down. And Spock didn't seem to be willing to slaughter hundreds of natives. Why should he be? You expect him to decide to wipe out hundreds of lives who may only be guilty of preemptively protecting themselves, and still keep his people in jeopardy because he felt like he could wait a few days for Kirk to get back? If my car got a flat tire in a dangerous neighborhood, I'd work like hell to get the spare on as quickly as possible rather than wait the hour and a half for a tow. I might even drive on the rim until I got clear of the danger area, even though I'm ruining it in the process.
I watched this episode again last night. After assessing the situation, Spock saw no chance of survival on the surface. None. The script was very clear on this. Getting into orbit increased their chances of survival since it's apparently easier to detect a ship in orbit than it is to find one crashed on the surface of a planet. Even if they failed, a quick death by burning up in a decaying orbit was considered preferable to the death at the hands of the hostile natives. It's all very well presented. They had no other option. You keep insisting they could camp out and wait six days. The problem is that nothing in the episode supports your assumption. They make it very clear they will not survive that long.