I think we will see Quantum again. For an era so reliant on continuity and character development, they can't not tie up the Quantum storyline. The organisation is great, it's just Quantum of Solace didn't really have a chance to show how shadowy they can be. I see Blofeld being introduced at the end of the next one, Tracy in Bond 25, and Craigs last, Bond 26 being a faithful You Only Live Twice adaptation. Then we can have Bond 27 pick up with a fresh actor and story.
Just going back to the idea that I was typing out when the site disappeared or crashed or whatever, but I really don't think that Quantum will make a return. Going with the idea that Craig's Era is dependent on continuity (I don't really think that it is, but for argument's sake let's say that it is), then Quantum would have most likely been dealt with by the time
Skyfall came around. If it hadn't been, then surely it would have been a topic of conversation at some point during
Skyfall. Since M and the rest of MI6 seemed so terrified by the organization during
Quantum of Solace, it only stands to reason that that fear would have grown exponentially over the course of 6-8 years if the organization continued to operate on a global scale.
I think what they'll do is retroactively go back and say that Greene and Yusef gave up enough information for Bond to get hot on the trail of the organization and ultimately take them down in the years between
Quantum of Solace and
Skyfall.