Justice would be done, I'd say.
Have Lincoln stick with Hamlin as VP, then you have the Radicals in the White House and running Congress. If anybody is going to punish the CS leadership for its crimes, it'll be the Radicals.
Do some googling on Hamlin.
He was a strong opponent of the death penalty, and campaigned for its abolition in his native Maine. He won't hang anyone except maybe the assassins of Lincoln.
Incidentally, rhetorical flourishes aside, this seems to have been the attitude of most Radicals. Istr reading that even Thaddeus Stevens, though more than willing to exclude ex-rebs from public office, once declared that were Jefferson Davis ever put on trial for his
life, then he, Stevens, would serve without fee as defence counsel.
The will for that kind of nastiness simply did not exist, and its hard to see how it could have been made to exist.