I think regarding atrocities, I rather doubt that the Taliban will be very specifically filtering on that, given their own record: nor do I think they'll care if any particular communities attack former government members, as that would from their perspective be rather good propaganda for themselves as "liberators". Members of the former government are probably in more danger as a result of their membership of said government, as far as the Taliban are concerned, than for any crimes they committed. I think the Taliban will also be quite willing to bring some people on board who are willing to come on board on their terms - again, regardless of atrocities. It's noticeable that of the opposition military leaders, they often have strong personal or ideological reasons to hate the Taliban or extreme Islamism generally, rather than simply being poor personal fits for the new regime (Saleh had family members tortured by the Taliban, Massoud's father was assassinated).
Also, from the best evidence we have available, for all its myriad faults the old regime was probably more popular than the Taliban are, at least among the bulk of the population around urban centres, and that may only be compounded if the Taliban make any missteps in the near future. And that might be even more the case with some especially grim figures: Abdul Rashid "Old Music and Whiskey" Dostum, for example, is very likely a war criminal but is at the same time very popular among Afghanistan's Uzbeks by all accounts.
I think the point on Karzai is interesting: besides the somewhat risky nature of any Afghan politics I'm not sure Karzai has quite the skill and capital of Talleyrand. I'm not sure how the violence levels actually compare for politicians as opposed to civilians: revolutionary France did have a lot of assassinations, not to mention things like the purge of the Girondins.
On a related note, it's arguable that Dostum and Atta Noor have been a bit more sensible in ensuring they weren't in the country
before negotiating, though given the failure of negotiations with Massoud it seems unlikely the Noor & Dostum factions will get any leeway with the Taliban.
Fighting in Panjshir seems to be continuing, with both sides claiming significant successes: it's really impossible to tell what's actually going on. Pro-Panjshiri twittter accounts have reported territory gains and hundreds of Taliban losses, whereas pro-Taliban accounts claim that most of Panjshir is now under control. It's perhaps notable that the Taliban forces have suggested a ban on posting videos from the area, nominally for operation security reasons but this might also imply they're covering up a slightly less rosy picture than they'd like to portray.