Revan will expect assassination, sabotage etc etc. because that's how crime lords work. To ward against such a threat he will likely do one of the following: lock down his vessel, no-one goes in or out without his permission or retreat to the Temple of the Ancients on Lehon, which is something of a natural fortress not to mention a hidden one. In both situations it suddenly becomes incredibly difficult for Xizor to kill Revan.
So you present two defenses here. Gonna start with the easiest first.
1.) Lock-down on Lehon
Makes no sense to the character. Revan would never do this. He's too strong, too driven, and too much of a figurehead to retreat. The last time he was in a war, was he hiding? No, he was on the front lines. Commanding from his flagship, not from some meditation chamber. He didn't hide from Jedi, there's no way he's hiding from criminals. Arguments that don't make sense to the character would never happen, and so shouldn't be evaluated.
2.) Lock-down of "his vessel"
A couple refutations:
a. What is "his vessel"?
Ambushing Revan's fleet is a major option for Xizor. If, as you say later in this post, Revan does not attack Coruscant, that means Xizor has his navy at the ready. Not to mention he will quickly be able to gather forces and underworld tech and employ his info network. Xizor could use a gravity well + his fleet + thousands of Black Sun forces + info network to strike at Revan's core fleet at its weakest. And Revan's ship, no matter how locked down it is, can't withstand the firepower of mass-drivers, torpedoes, etc. For sure if it's a standard-class battleship. And seeing as all they have to do is kill Revan, they could focus solely on his ship, all they have to do is kill it and they win. And Xizor would be across the galaxy, out of harm's way and still gathering forces in case it fails. BOOM Scenario.
b. Lock-down? Psh.
I was under the impression that ALL war ships were locked down during like.... war. But Star Wars assassins are something else. There are other ways to get into a ship than through the airlock. Using the info network to locate Revan's fleet, and stealth tech to get them there, IG-86's and/or other assassins could easily make a space jump to the hull. Revan's ship will have to stop to refuel, resupply, and reevaluate, so there will be plenty of oppertunity, more so as time drags on. It would be simple to either 1.) cut into the hull/break a window (Bridge?) and storm the ship, 2.) go for the engines/auto-destruct, or 3.) attack the engines themselves via spacejump without even setting foot inside. BOOM Scenario.
Instead he will likely send assassins to scout the area, if Xizor is there they've got a pretty good chance of killing him. But if Xizor has retreated already (more likely scenario) they will find nothing and report back to Revan. Which means Xizor's decoy will fail (did I just argue with myself there?) That's all I've got for now. I leave you guys to come up for counter points for Xizor and Revan supporters to come up for a death scenario for Xizor...
Yes, Xizor will desert the place as soon as it starts.
And this scenario (discovering the decoy) only gives Xizor his fleet at full power and lots more time. So if this truely is how it would happen, it only helps the Dark Prince.