Sasori, le't him self be kill, Choyi"grand" told Sakura, i guess he was tired of life, and i understand him, he had a bad childhood,Itachi-I want to see his true power, if he was simply playing with sasuke id love to see what he would do in a real fight.
Sasori-He was cheapened a lot.
1 poison dart and youre out, the only reason he got beaten was because granny chiyo knew most of his moves.
Even someone as skilled as oro or jiraiya would have trouble avoiding them needle sprays because theyd never have seen the attack before.
sasori is incredibly powerful, unfortunately he was up against the worst opponent possible, plus sakura had time to make antidotes, in a real 1vs1 contest no preliminary planning, sasori could wipe out tonnes of ninja, he even defeated the considered strongest kazekage ever.
Pain-I dont know if hes dead, they never really said, but im assuming he is, because he'd have been a great help towards kicking akatsukis ass if he converted to narutos side.
I think every villian become villian because of their child hood, they want to have something they never had, or soemthing they lose.
Sasori, love "he make puppets of his parent"
Nagato, become power to make peace"and stop his friend from dying"
etc