This is an interesting and difficult question. I'm not a pension expert, but my understanding is that there are a variety of options, including bridging, that can get from the point of new employees coming in to an ultimate solution with a go-forward pension plan for all, but I'd be in speculation mode as to which option the contractor would choose to put in place.
Evidence of meeting #38 for Natural Resources in the 41st Parliament, 2nd Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was employees.
A recording is available from Parliament.