It never just occurred to me until now, but I just got to Gaines's death episode where Gaines told Kevin that if you fail the Drazens or try to leave them, they WILL find you and kill you. That's why he was so confident Jack could never protect him despite the offer.
Now, Jonathan Matijevich was unable to kill David Palmer, the job he was specifically hired for. Yes, this was due to Jack's interference by grabbing Alan Hayes's gun, but he disappeared after that and Andre sent his brother Alexis to kill Palmer in his place, why?
It is specified he escapes, and that CTU agents were looking for him, working out that he was involved due to deducing the real Martin Belkin's fate. It is also specified that he never got back to Gaines after the assassination attempt. So, obviously he ran and left the assassination attempts. He ran from the Drazens' plan.
Is it possible that, either due to his "failure" or never returning to Gaines to take part in a second assassination attempt, that Andre had him killed? (If so I'd like to think Jovan Myovic carried it out, he was also an assassin and arrived in the US two days ago, and Alexis didn't arrive until later.)
I mean, yes, they didn't hunt down Rick after he betrayed them, but from the sound of things Gaines hired Dan first and Dan got Rick into it, so he probably didn't even think him worth mentioning to the Drazens, and if he did, Gaines was likely planning on killing Rick once he was no longer any use to him. Thus, either Alexis didn't notice him missing from the remainder of Gaines's crew when he killed them, or they didn't have enough information on Rick to track him, or else decided to leave him until after they got their revenge. Jonathan was the sniper who was going to assassinate Palmer and frame Jack, which was the Drazens' ultimate scheme, and ran off after Plan A failed. And the Drazens did have a few assassins to spare before they stepped into play.