A post-Cold War role for Violet Friend missile defence

What could keep a deployed Violet Friend anti-ballistic-missile system from being retired after the Cold War?

Its value against limited attacks by smaller states could preserve political freedom and justify keeping the system.

The question assumes that the British Violet Friend anti-ballistic-missile project entered service. No practical defensive system could absorb the full mass of a superpower attack with numerous re-entry vehicles. Its more durable purpose would be stopping a limited launch by a smaller state or other isolated actor. Intercepting that weapon before it struck would preserve political choices that disappear after a successful attack. Missile defence would therefore raise the threshold for coercion even after the original Cold War confrontation ended.