To be honest, I don't think there's any chance of either Go Ahead or Stagecoach being allowed to buy Arriva (in parts or as a whole).

If they still go ahead with selling it, it'll probably end up being some Asian investment firm that buys it, and IMO that'd probably be for the best.
To me anyway, the main issue with Arriva is lack of investment, if a company with all of the money buys it, they might invest in renewing the fleet, training the drivers properly, or getting a customer service department that know what customers service is!

If any of the other big operators buy them, are they going to spend money on them? I don't think so, I think what would happen is they'd stick their logo over the Arriva logo and that'd be the end of that