Well, ironically, this predicament was addressed this morning on Fox News with former astronaut and Fox News contributor Thomas Jones. (He along with Robert "Beamer" Curbeam installed the Destiny
lab back in 2001.)
He said that a couple things cold happen, well, really only one when you get right down to it.
First he was asked if any other country/agency (like mentioned here in this thread) could supply a vehicle until Orion gets up and running, but he said there's nothing that could be available for years to come so it wouldn't solve the problem.
But ultimately he said that the shuttle program could be extended on a limited basis (like 2 missions a year for resupplying and crew rotations), and putting a fast track on the Orion program. Getting the thing operational a year or two before it currently is scheduled now.
But all of this of course depends on if Russia decides to continue to support the ISS mission. Jones said that he doesn't think Russia will change its support for it, but you never know. If this situation gets otu of control, then all bets are off. Like I said, we may seeing science fiction become fact before our very eyes...and that'd be some major foreshadowintg 24 years in advance.