I can't see how any ofcom related enforcement could result in 2 out of three channels of a broadcaster being removed from the EPG as any 'dodgy' content that resulted in action being taken could easily appear on the other 1 station.
As far as the legality of the situation goes they could have taken action in the form of a 'cease and desist' type affair which could have forced sky to encrypt\block transmission but that action would (unless the lawyers involved where complete numpties) be aimed at the producers of the station rather than the broadcaster, especially following the situation that someone else mentioned whereby Playboy got fined for the actions of another company as the other company produced the content while they owned the rights to the broadcast channel on which it was shown.
It just doesn't make sense for 2 of 3 stations to be taken off air.
I would go so far as to say that it all comes down to a mistake with the upkeep of what channels are live and that resulted in Sky removing the channels from the EPG. I also very much doubt a channel would bother to produce a show if it was going to be inaccessible a couple of hours in and especially if they had knowledge of any legal issues unless they where trying to appear as if they had not been notified of any problem.
If Sky\Ofcom took action without some form of confirmation\acknowledgement by an offender or at least made a statement explaining that had received no notice from the offender and where proceeding with it's actions, they would be leaving themselves open to counter action of some kind and so I doubt that was the case either.
I only hope that when everything is sorted that BangMedia (assuming they aren't at fault in some way) don't get given a hard time by Sky if they, BangMedia, decide to seek compensation for loss of business, as if the blame game starts, the legal wrangling could cost more than the lost revenue of the 2 channels.
Sky could potentially take the blame but say that the station's where accessible via other means that BangMedia could have advised their viewers to watch via the 'other channels' or via the web etc. to minimise any fees they could be liable for.
It's all just speculation and conjecture at this point so we will all just have to wait and see what happens next.
UPDATE: That all being said, I've just read elsewhere (on another site) that 902 is licenced from Playboy and so that could explain why 902 is still on air if there is some form of ofcom action in play (perhaps those lawyers are numpties after all!). There is also mention of a circa £160k fine for past infringements which BangMedia haven't paid which could have resulted in a mandatory loss of licence and subsequent removal from the EPG (until the fine is paid).
That makes some sense as in that it is easier to remove to a channel from the EPG as a temporary action and once the fine was paid service could be restored which is all in all a better scenario that Sky bothering to sever all ties\feeds with Bang' only to have to re-establish them later (probably at their own cost) once the fine has been paid.
Again all just speculation and conjecture but another possibility none the less.