I am not sure that there is "absolutely no sense" in maintaining the status quo but, with the amount of military flying going on in the UK these days, there must be a break-even point approaching. If the DOT is going to provide an equivalent service to which we have access, then someone in MOD is going to come to the conclusion that a bespoke service based on a military helicopter is luxury we cannot afford. The loss of the capability will be bad in many ways but I guarantee that many of the crews will find themselves in Coastguard uniforms or transferring their skills to the SH Force, carrying on the in the finest traditions of the SAR Force.
As for CSAR - no chance. MOD will not stump up the resources in pers, airframes or raw cash, IMHO.