No, it won't happen because their chances of ultimate success are slim to zilch and the risks FAR outweigh any potential gain.
As to the (very good) question you posed: would a launch of such "EMP birds" over our country result in a nuke response? Yes. Absolutely. We won't wait 'round to determine what kinds of birds they've lobbed our way. That is a fact.........and we'd know where they're headed the minute they've launched.
Here's a hypothetical one to ponder: Let's say we expand the war to Iraq. Our forces are divided between maintaining order in Afghanistan (with help from England) and conducting air strikes in Iraq. We have a lot of firepower in the region, but it's pretty well commited to Iraq and Afghanistan. China makes their move and takes out our satellites. Command and control of our forces in the Persian Gulf area take a big hit. Without GPS, JDAM's become very expensive un-guided gravity bombs. The only way to monitor Iraqi troop movements is with unmanned aircraft like the Preditor since we no longer have satellites. The situation is not good, but not impossible to deal with. Then we have a little surprise...North Korea charges through the DMZ and over-runs our forces. Then China launches an envasion of Taiwan.
Back in the US, the stock market is doing a repeat of it's post 9/11 dive, that is, if the markets have been able to re-open. Television networks are scambling to buy time on the few remaining communications satellites over the continental US. Commerce is at a crawl because credit card transactions, pay-at-the-pump have to be called in manually and the companies that handle authorizing those transactions can't handle the amount of calls. Most automated teller machines are out of service. A few years back, there were some studies done on the damage to our economy if a series of solar flares or meteor showers took out our satellites. I believe the effect was in the neighborhood of several trillion dollars in lost productivity and commerce which could cause a long financial depression. With our economy in ruins, it would be hard to keep the military supplied. And all of this is if there isn't a thermo-nuclear exchange. I'll be the first to say that the possibility of any of this happening is remote at best. But at this time last year I would have thought the same thing about the chances of four passenger jets being hijacked in the same hour for kamikaze attacks on the World Trade Center and the Pentagon.