Even if that happened... they Islanders are still in a far better financial position. They'd own and operate an actual hockey arena.
The Islanders have never gotten all of every revenue source. They didn't get concessions or parking or all of tickets in NVMC. They don't control all their revenue in Barclay's, they get a flat rate.
They'd get 100% of advertising, signage, concessions, suites, tickets, sponsorship, local TV and national TV revenues from Islanders hockey, AND they'd get extra income from non-hockey events at the arena.