Bosch in all likelyhood knew all there was to know about the readiness of the Colossus - he did have a saboteur planted on board, after all, for when it tried to prevent him from passing through the Knossos portal. As has been mentioned though, he probably just didn't care about it as long as it didn't directly interfere with his plans for contacting the Shivans. Nor did he care much for the NTF or their fate, as long as they kept the GTVA attention off his real plans for long enough to carry them out.
Nor do I remember seeing any indications in the campaign that he is actually opposed to the GTVA as such, rather than just fighting them out of necessity due to them being in his way, and as such he would have nothing to gain from destroying the Colossus. It would just weaken the GTVA against the Shivans, which despite his ETAK plans I doubt he would want. After all ETAK might fail in contacting them, leaving war as the last resort. And he doesn't seem to be after the destruction of the human race, but actually rather seems to be seeking a non-violent way to end the conflict.
Of course that doesn't seem very likely with the Shivans, but still, we never found out what happened to him so I guess you never know. He could be in some distant system trying to convince the Shivans to just let the Terrans and Vasudans have their little solitary bubble of space to themselves right now. Perhaps that's even why the Shivans blew up Capella, instead of just sending those 80 Sathanas through to Vega or Epsilon Pegasi...