For those quoting 13.1...
Since CPA services would be continuing at bases which operate the 747F such as YVR, YYZ, ORD, LAX etc etc, section 12.1 would be more applicable.
If they did want to completely close a base OR should they wish to reduce the overall crewing level at any of the above mentioned bases then it would happen in reverse order of seniority. Note, many Freighter pilots are more senior than the most junior Pax pilots at their base. Remember, ASL is not rank specific so a Freighter CN could bump a junior Pax CN or most FO's.
I don't think CX wants to open that can of worms!