There should never be an island actually separated from the rest of the land. If that happens, it's a bug.
But note that there is a newer, much better version of this game available for download (to play in Mini Micro, which is also free) here: https://miniscript.org/MiniMicro/dlc/
That version has background music, post-game power graph and speed replay, better land generation (plus a selection of built-in maps), better AI, and more. If you're enjoying this game, please give that a try!