The nearest port is Biera which is 250 km from Zim's eastern border across Mozambique. The nearest place for a naval task force is the Mozambique Channel.
In a military adventure, logistics is determinative.
Any expedition into Zim will need the acquiescence of South Africa or Mozambique and probably both.
An ostensible expedition to extract British and Commonwealth nationals has probably gotten the nod from Mbeki.
An ostensible expedition by a former colonial power to take out the revolutionary president of an African nation will never be accepted anywhere in Africa.
Sometimes an "ostensible" can lead to a different actual "for reasons of operational necessity".