ONCE UPON will play a Nederlander house unless plans have changed very recently. (And Nederlander is producing it.)
INTO THE WOODS would be silly to play the Sondheim if the St. James is an option. Symbolism be damned, they can earn a lot more in 8 weeks at the St. J than at the Sondheim.
I wish the Roundabout would move 1776 to the Sondheim instead of the Airlines. The Airlines is not a great house for a musical.
Regardless, there are plenty of shows waiting to come in. No doubt a new tenant will be playing before year's end or sooner.