The MBA is insanely durable. Provided it meets your performance needs, I believe there is a good chance you could get several more years out of it.
Before investing money, you could take the MBA (along with the charger) to an Apple Store or Apple Authorized Service Provider and ask them to run MRI on the machine (it's free.) This comprehensive diagnostic looks for many of the most common signs of hardware failure, and will specify which specific areas have issues (if any.) This might be nice piece of mind to get the machine a clean bill of health before investing the money in it?