Vernet sought the permission of the British consulate before establishing his colony – clearly even he thought there was ambiguity over the status of the islands.  Moreover the British and Spanish settlements ended not because of commercial failure but because of indirect pressure caused by war. If Argentinian sovereignty survives expulsion through war then presumably British sovereignty could survive temporary abandonment due to war.  It is also difficult to describe a settlement as permanent when it was on the point of collapse when the British took it over.