Well, if we beginn with that we can construct a whole relation screen where it is shown the probability of them betray you . It would be influenced by their Ethos, by the " rapport de force" (I don't know how translate in english, but it is a comparaison between your strength and their ) , the regularity with which you paid them, your amount of money, the advantages you give to them (plunder taken planets, high rewards etc ) , the time you employed them (if it is long enough they might become utterly loyal, like the Varangian Guard which was loyal to the end and they defend succesfully their part of Constantinople in the 4 th Crusade despite the collapse of Byzantine forces ) , and if they are loyal they might lower their money exigences etc. There is a whole idea for a DLC there.