I have August 14 temporarily marked in my book for a permanent Doubtfire closing. It’s before the kids go back to school, and before the show premieres overseas in Manchester.
While I agree that it's unlikely the show lasts beyond Labor Day, I wouldn't view Manchester or the kids in the cast as a factor. There's no need for the creative team in New York, and Bway costumes/props could be saved for a US tour.
Manchester (the start of a UK tour) is a separate capitalization for which building costumes would be a budget line. Raising money for the UK production would have begun months ago, and if they were to indicate in offering papers that they're shipping/repurposing Bway costumes, it would be announcing the failure of the Bway production. And not to split hairs, but August 14 would be cutting it too close for a September 2 start of previews in Manchester (assuming laundering, sorting, shipping, fittings for 29 people, and 10+ days of tech).
From a casting notice posted recently, it seems Zachary Dietz is no longer continuing with the production; Matthew Smedal will assume the role of music director / conductor.
ErmengardeStopSniveling said: "While Manchester (the start of a UK tour) "
I'm led to believe that following Manchester, the show has already booked into a mid-sized West End musical house. There is certainly a lot of love for the film in the UK so I think it should do very well here.