He's not lost without them. The Mandalorians made a foolish attack on Onderon after Ulic was captured. They had absolutely no support from Kun's forces, and they were defeated. Then Ulic lead the Republic to Yavin 4, where the Jedi imprisoned Kun's spirit. Ulic's capture caused the end of the war. Without Ulic, Kun has no need to worry about anyone leading the Mando's to him. He can do as he pleases. We saw Exar Kun have his way with the galaxy until Ulic was captured and the Mando's were defeated.
Seems a bit foolish on Kun's part to remain on Yavin 4 undefended... how did the Republic fleet managed to invade Yavin 4 so easily?