Mass Effect 3 outsold both ME1 and ME2 without assistance contribution from Game/Gamestation. And while it could be argued that ME3 is high profile enough for people to shop around for it, the same can't be said of Mario Party 9, yet that placed third in the games charts the week of it's release, outselling previous Mario Party games during their first week.
One of the main reasons Game/Gamestation are dying is because people are now savvy enough to shop elsewhere for better deals, be it supermarkets or online.
And as for publishers, many of them WANT to see Game/Gamestation die, as the pre-owned market cuts into their profits significantly, and Game/Gamestation focus a lot more on pre-owned than they do new stock. There's a reason why EA were the first to pull support, when they're the publisher who fight used game sales the most (online activation codes in all of their games). Game/Gamestation's precense likely costs publishers more money than they make.
Also, as JoeTheBlow stated, Gamestop won't buy them out. If Gamestop do want to establish themselves in the UK, they'll wait until Game Group go into administration, and then set up afterwards.