What "Carlos Marik" are you talking about since there are two men of this name?
The former. The Captain-General.
Captain-General Carlos Marik probably simply died in Canopian exile, be it either due to old age or Canopian government disposed of him ... Or perhaps he commited suicide. But no big mystery here.
Most probably. But when heads of government enter exile in the real world, we usually know where they've landed (if not their exact address), and they usually lead some opposition or at least remain in the public eye.
Carlos just disappears with his last known location being the MoC. That opens up possibilities beyond a quiet death offscreen.
For example, we know he escaped with one loyal "ship". What if that "ship" was a warship? What happened to it? What did Carlos do with his warship before he met his end?
Or, instead of leading a public opposition, did Carlos ally his assets with one of the underground FWL/Marik boogeymen of that time, like House Selaj or the Sian-Mariks? Is some measure of the FWL's lack of unity and political fracture lines due to the machinations of someone like Carlos pulling strings from the shadows?
I'm not saying that any of these things happened or are even probable. I'm just saying there's a blank page in the canon FWL history that some interesting stuff could be written into.
FWIW...