I think Boothe did the Southern States and subsequent history no favors by assassinating Lincoln. I find it quite likely that the disasters caused by his pursuit of the war would have come back to haunt his legacy, but instead by killing him, it strengthened the power and increased the fanaticism of his political party. (As it did in the Kennedy Assassination.)
Just as Timothy McVeigh got Bill Clinton re-elected, so too did Boothe's bullet keep the horrors of Federal tyranny from getting a fair consideration. It was one more ill thought out move in a series of them.
I don't think History would have been kind to Lincoln had he lived.
“horrors of Federal tyranny” - hyperbole much?