On Coruscant, Ulic and Mandalore will lead the Mandalorian and Krath armies against the Black Sun, destroying all opposition. Once inside, Ulic and Mandalore confront Xizor (who didn't have enough time to prepare for the attack) and Guri. Ulic will quite easily defeat Guri and Mandalore will kill Xizor.
If Xizor knows who he's up against, I assure you right from the word "GO" he'll be burning lines trying to get away from Coruscant and his almost-defenseless palace. He does have a fleet and a personal ship. I think Kun will be forced to face him in a space battle. He certainly won't be unprepared for Kun's attack. And hyperspeed isn't a split second and you're there.
Also, I think Guri could kill Mandalore.... but not Ulic, obviously(?).