Best case? Nothing. Worst case? This time next year, the iAd platform is like most other high-paying ad platforms—overrun by ads with blinking banners telling you that you have to install Java to use them, with clicks taking you to malware sites. Most likely case? Somewhere in between.
If I were shipping software and depending on iAd for revenue, I would at least be talking to other ad networks, doing A/B testing with their ads to see how customers react, and generally having contingency plans ready just in case iAd crashes and burns over the next few years. Then again, if I were in that position, I would have already done so years ago, and I'd reevaluate things at least once a year so that I'd always know what the landscape looked like at any given moment, just in case.