Cold-weather sloops as a durable patrol fleet

Would Cold War cold-weather sloops built for fishery patrol have been retained for other Royal Navy duties?

Probably: new, relatively inexpensive patrol ships could be kept while costlier ships were withdrawn.

Purpose-built cold-weather fishery-patrol ships would probably have been retained. The Island-class offshore patrol vessels are the precedent for that expectation. Slightly larger vessels could remain useful as new ships with modest operating costs. Keeping them would allow the navy to withdraw more expensive ships from service.