Interesting and valuable questions and discussion....
I think you will find hikers and hiking partners with varying degrees of helpfulness. There are those who will hike with you only if you can keep up with them, and they won't wait at any trail junctions, or any other place. They just keep going on their own. I prefer not to include that type in any hike I organize or join.
(Reminds me of this: Hiked with a guy like that once. He left everyone and went ahead, both going in and out. Going out, he got off route; nobody called for him, just kept going. He made it out after the others, and was complaining. I was laughing inside. Will never hike with him again.)
Now your friend DID say he'd help you out if you got AMS. I am thinking that you would probably get the AMS on the way in, and turn around. If you are not actually becoming HACE-like (slurred speech, dizzy, etc), but only nauseated and unable to eat, I'd think turning you around so you could head back alone should be ok. You can't really lose the trail in the daylight. Partner could continue on to summit, and on returning, accompany you the rest of the way out. In fact, if anything happened on the way in, and you are still able to walk, then sending you out alone, with the idea of summiting and returning to help finish the exit, would seem ok. Just remember that in any of these situations, the slower hiker should always stay ON the trail, or within easy sight of the trail (only getting off to get water, etc.). If anything else, like a toilet stop, leave the day pack ON the trail, so the other party would stop. You should plan and agree on this before you separate!
However, if these "friends" are the sort who would leave you in their dust, head to the summit and exit, without ever joining you on the way out, then you are basically planning on hiking alone. If that is what they intend, and you should find out now, then make sure you know ALL aspects of the hike. You cannot depend on these people for anything. You need to carry all your food and snacks, know where to get your water, carry your own first aid and medications that might become necessary, AND hike wisely, knowing when to turn around. There are way too many stories where hikers hurry out, leaving their slowest member behind, then start whining to Doug at the store that maybe a rescue is necessary. Leaving a slow hiker on the trail can only lead to trouble.
Hiking partners should accompany the slowest ones out. If needed, stronger hikers can even carry the slowest hiker's pack. (I get pretty annoyed when the slowest refuses to give up some weight, and continues hiking out ever so slowly, delaying everyone's exit.)
Having said all that, you won't be hiking alone on the Main Mt Whitney Trail. With over 200 people per day permitted to hike, you should be ok. If you ARE hiking alone, then talking to others on the trail can help. You might be able to help someone in need, or should the opposite be the case, you can likely get help if that is necessary.
