Was the intent to use the AOPS to replace the MCDV's. I hadn't heard that before. Those 2 ships may have similar abilities but they also have significant differences.
Leadmark 2050 and the Defence Policy don't seem to plan on replacing the MCDV's with the AOPS. Like you said there are significant differences largest of which is the cost and crew outlay. MCDV's are in particular really excellent on the West Coast and Caribbean.
What is the plan to replace the MCDV's?
There isn't one. IMHO the priority should be on replacing the subs well before the MCDV's.
I guess the worry then, is if anybody will actually see the end of the MCDV’s as a crisis. By that, I mean, nobody outside of the RCN or chat groups like this one, know what that type of vessel brings to the table. So, if ultimately John Q Public and the government see a half dozen AOPS and 15 CSC, will anybody “important” even realize anything is missing once the KINGSTONs go?
Is losing them a crisis if their jobs are taken over by other ships?
Honestly I have no idea, time will tell once the AOPS are online. The MCDV's are moving past their halcyon days. With AOPS on the way taking over some of those jobs and the frigates finished FELEX (essentially) they don't have to plug gaps like they used to. Also with the JSS, AOPS and CSC on the horizon no matter how distant there will be a crunch for bodies to sail. The fleet will go from 24 surface ships to 31+ ships even before the CSC start hitting the water. I can easily see MCDV's being the first platforms to be pillaged for people. I see the most likely end of the MCDV's coming from personnel issues, even before the ships get too old.
The other option I see is a consolidation of the MCDV fleet into less hulls and a refocus on Mine Warfare/ route survey. Getting them to really do the job they were originally envisioned to do. I have seen a shift in the Reg F navy's awareness of mine warfare since it became their responsibility. The ships, as stated here before, are in pretty good shape so they are expected to last a while.