what if I exceed in 1000 maximum cycle count in my MBA battery?

There is no "maximum cycle count". 1,000 cycles is only the estimated count for full performance. You battery will simply hold less charge as time goes on. It won't suddenly stop working. If you battery does need to be replaced, Apple will replace it for you. Their charge is reasonable in that it runs about the same price as removable batteries in the older machines... only they'll take it apart and replace it for you.

To add to Joey's excellent response, a quote from Apple's support website:

http://support.apple.com/kb/ht1519

"Batteries have a limited amount of charge cycles before they are considered to be consumed. Once consumed, a replacement battery is recommended. You can use your battery after it reaches its maximum cycle count, but you may notice a reduction in your battery life. Knowing how many charge cycles are on your battery and how many are left can help you determine when a battery replacement is required. For optimal performance, replace your battery when you reach the maximum cycle count."

The cycle count is just there to determine warranty eligibility; batteries past the maximum cycle count for that model are ineligible for free replacement, regardless of whether they are covered by AppleCare or hardware warranty.

You choose when to replace your battery, based on performance. If it is still performing sufficiently well for your uses, then just keep going until it no longer does meet your needs. For some heavy battery users, that may be less than 1000, for some it will be more. Cycles really do not matter - capacity and performance are all that matter.