In consequence, departed after island cut off (7)
I believe the answer is:
isolate
'cut off' is the definition.
(both can mean to separate from others)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for isolate that I've seen before include "Segregate. close off" , "Place apart, away from others" , "Place apart from others or alone" , "Place or set apart" , "Eat soil (anag)" .)