It looks like Gattelli was still involved at of the beginning of March. He'd done previous workshops and was still discussing the show. Who knows what happened, but Grandage did work with Ashford on the recent revival of EVITA.
I'm just curious if anyone here knows of possible contractual issues in an instance like this. With a show this big I'd think that Gattelli had some sort of agreement to date with workshops, etc. Perhaps he received a buyout or a royalty agreement? Either way, I imagine it has to hurt to lose a (possible) huge payday with a property such as FROZEN.