It probably will do ok, but there could be some side effects, not necessarily negative.
The engine and computer have been designed with high octane in mind to achieve the rated power and performance. Using less than high octane will cause the computer to dial back the timing as the lower octance fuels will likely start to cause some ping/engine knock. It will dial back as much as it is allowed if necessary. Whether it will be enough depends on the individual circumstances, driving habits, phase of the moon (kidding on that one).
Dialing back the timing will normally result in slightly lower hp and possibly even slightly lower mpg. The only damage that would be negative would be long term from the ping/knock if the system can't compensate for the lower octane fuel enough. Engine knock or ping is never good for an engine in the long run.
You probably could try a couple tanks of regular unleaded out and see how it goes. My guess is that you'll probably have better luck on midgrade. Just keep an eye (or ear) out for engine knock/ping and up the octane if you hear it.