You forget that Luke Skywalker contributed to the final Wall of Light that sealed Exar Kun away. Of course Exar Kun didn't accomplish what he set out to do, but he did far more than Malak did.
Ah yes, he waited a thousand years, planning his meticulous revenge, only to be trounced by a bunch of novices and the spirit of his own master. His 'plan' ended in failure. And even if he had survived the Wall of Light or Luke's Praxeum, his destruction at the hands of the Jedi Order was nigh inevitable.
This is what I don't like about Kun, for all his power and skill he achieved bantha poodoo, at least Malak accepted that.
But anyway, Malak accepted his defeat. In this sense, I believe that he was redeemed or, at least, on the brink.