Malak's final words after Revan/you kill him in KOTOR are: "As the darkness takes me, I am nothing" You can see the wreckage of the Endar Spire on Taris. There's also a republic quest line relating to the exiles who Revan helped while there. On Corellia as an Imperial there's a passing mention of the "Onasi Memorial", presumably memorialising Carth. Regarding Revan's plans though... the Extermination Droids are designed to kill anyone with Sith blood. Other races and Sith have interbred to the extent that 99.97% of the population of the Empire have Sith blood. So its not just the Sith Lords they're going after; they're going to kill practically every man, woman and child in the entire Empire. That's well and truly jumping off the slippery slope. Also, in the Foundry Flashpoint, the fight ends when Revan i's on about 2% health; further suggesting he'll be back.