That was recently confirmed - the cash shop was not only a plug-in, it was managed by a 3rd-party company. So we would just need a new plug-in - something the new owners would be very highly motivated to do.
Correct. Not sure of the original vendor, but middleware agencies like that are a big part of current game development. Why build your own in-game store when you can get a license at a fraction of the cost? CoH was very much scratch-built at the start, but I know at least the marketplace was 3rd party licensed.
One obstacle-- different vendors have different API's. We (well... they, but I'm a "we" in spirit) won't have access to the source code to alter the API's to a new vendor's system. If we don't go with the original middleware vendor, we would likely be limited to making a "wrapper" that would exist between the marketplace and the game. the wrapper would interact with the new vendor's apis and translate it to the old vendor's format that the CoH engine is expecting. Depending on what values are expected and security measures are in place, this could be quite the enjoyable challenge.
A less likely risk: some vendors consider their API interfaces to be propretary, meaning they could object to us using them... even if we just want to do it via "wrapper" to get around the source code limitation. This is unlikely to stall the project, but vendors can try to eke out fees that are less than the legal costs to challenge them. this is becoming far too common in the industry, but we'd be 'small prizes' and may not be worth the effort.
It might just be that they run the game with the in game store just generating an error, then manage access to the game and resources through a more manual interface-- run a "donation paypal" account with various rewards that you set through a custom-made interface to the existing db. More cumbersome, but depending on the middleware interfacing issues and costs, may be more do-able (and similar to what some emulator communities are doing).