Island to leave by boat possibly (6)
I believe the answer is:
tobago
'island' is the definition.
(Tobago is an example)
'leave by boat possibly' is the wordplay.
'leave' becomes 'go'.
'by' means one lot of letters go next to another.
'possibly' is an anagram indicator.
'boat' with letters rearranged gives 'toba'.
'go' put after 'toba' is 'TOBAGO'.
'to' is the link.
(Other definitions for tobago that I've seen before include "Trinidad companion island" , "Trinidad and - (WI)" , "Island near Trinidad" , "Trinidad's smaller partner island" , "island location" .)