In goal, Ilya Sorokin's eight-year contract extension kicks in next season, so he will be on Long Island for a long time. This offseason is about getting rest and getting his game back. Judging by his track record, Sorokin is likely to rebound back into an elite goaltender, which would be the quickest way for the Isles to remain in contention. Semyon Varlamov has three years left on his contract, so he is also going nowhere. Expect the Sorokin-Varlamov duo to continue in goal for the next few seasons.
The next roster area to look for change is on defense. However, Adam Pelech and Ryan Pulock are signed for five and six more years, respectively, and are lifelong Islanders who gave up some leverage to sign these contracts a few years ago. It probably would not reflect well on the organization to just dump those guys, and both of them have no-trade clauses in their contracts, so any move involving them would involve their approval.
Assuming Pelech and Pulock cite their no-trade clauses and remain with the team, the top five defensemen on the team would basically be assured of returning, save for a really unexpected trade. Scott Mayfield signed a seven-year contract last summer, so he is realistically not going anywhere. Alex Romanov is under contract for one more year before he will be RFA with arbitration rights next summer.