I can't even remember why Xerohour left. I think he left of his own accord, but after he left he made a stink about the mod still using his website graphics - which were made for the mod in the same way that models , textures, code etc etc were. We decided to keep the graphics when we switched websites, so Xero decided to direct the original site to that Star Trek site, instead of this site. Xero is actually a decent bloke, he just tends to get stressed too easily.
As for why Vader was kicked off, I believe it was because Xero and a few others felt that Vader was revealing info about the mod , to the public via interviews etc, without talking to the team 1st (Some things the team hadn't even discussed etc). I can't remember properly, nor was I much involved since I had only just joined (must have been about 3 years ago) , but I do remember that Vader was the guy I PM'd about joining the mod
. Infact, it was an interview with Vader - showing the Xwing - which I stumbled upon while browsing for a new modding adventure.
BTW, Vader, soon after you left the mod, Xero found , or atleast he believed he did, you bad-mouthing the mod and team, on some website. Was he right? 
"Government is the great fiction, through which everybody endeavours to live at the expense of everybody else."
Frédéric Bastiat