How British guided weapons might evolve

Would a retained Blue Slug evolve, and what could replace Short Hellcat?

Blue Slug would probably gain an improved version; the replacement choice would likely be a British missile, Exocet, or Harpoon.

A missile retained in service would likely evolve through an enhanced Mark II-type development, regardless of its eventual name. Continued adoption would create pressure to improve the weapon instead of freezing its original configuration. Before the later helicopter-launch clarification, the possible Short Hellcat successors are a domestic British missile, Exocet, or Harpoon. The launch-platform clarification at 1:12:58 changes that answer and points to Sea Skua instead.