I agree with the majority of this, especially the boys' motivation to hide an OD. In terms of LS possibly wanting to buy more coke, etc., I think it depends on the personality. There are users who can't stop ... take John Belushi. He went back to his room drunk, vomited, and went back to partying. The woman who gave him the fatal speedball was charged and convicted. But he wanted to keep on partying. I'm not sure LS COULD have been out looking for more, but she might have TAKEN what was offered.
And the boys might have freaked if that happened (perhaps justifiably so). Similar to Belushi's death was musician Tim Buckley's: a friend, ticked because an intoxicated Buckley interrupted him having sex, put some heroin on a mirror and told him to take it all. Buckley, described as "rebellious," did just that ... and died from a heroin/alcohol overdose. That friend was also tried and convicted. I agree we need to try and get into their heads, but w/o knowing the personalities, it's hard, IMO.
I'd like to think that LS wasn't looking for more and that the boys wouldn't hide an OD. But as you note, none of them may have been thinking rationally. The bigger issue I have, actually, is how they could have hidden her body so well if that's what happened. Unless they just got lucky. But as well all know, luck usually runs out.
PS: Charlene's letter is haunting and heartbreaking.