Wayne would know better, but I'd bet that Merion had some pretty good arrangements with other local clubs during the period in which it was closed. In Canada, when Hamilton held the Canadian Open, the members were able to play places like Magna, St. George's and the National while the club was closed. Given a club with the prestige of Merion, I'm sure the members didn't have issue finding games.
That would have made it much easier for them to deal with the course being closed, I'm sure.
I think this is a factor people forget when considering whether the members were happy holding a tournament.
What's the cost of holding the US Am? Well, if a place in history is a cost, I guess Merion is paying dearly.