i was looting a reactor and died, luckily i had the great idea to remember the coordinates before i went inside. so i returned and died a second time. each time i didn't lose my island or syncs, but when i do /mode it says i'm on hardcore. i'm not sure if this is a bug or not, but i'd rather not randomly lose my island when i log on one day.
If you are to far away from your sync station and it is not chunk loaded it will not work. Your island would be gone if you wouldn't have experienced this issue.