No real reason to call US; Barclays is more or less US' customer, who just buys the miles on behalf of the credit card customer. US won't be able to overturn Barclays decision and if Barclays decides to revoke the miles, US won't be in any hurry to give you the 40k miles from their own budget. Barclays will need to initiate a debit of miles, so if you decide to call US anyway it won't expedite that debit. But I'd imagine, sooner or later (and probably at the next billing cycle sweep) Barclays will indeed take those miles back; they are quite good at reclaiming their miles when you return something for a refund.

As far as your award ticket goes, I'm not sure that I'd risk it. If Barclays pulls the miles quickly, you won't be able to ticket, that's pretty straightforward. What I'd be concerned about is what happens if the account is emptied to book the award ticket, then the Barclays debit comes through. I'd say there's a chance that you're able to fly anyway, and come home to a US account with a negative balance, and just create a new account and go on your merry way; but there's at least an equal (and probably greater) chance that the Barclays debit puts your US account into negative balance, and US cancels the ticket. YMMV but personally it is too much risk for my blood.