"In the event that the Customer shall sell, or otherwise dispose of the land and premises, or commit an act of bankruptcy, or allow a judgment or lien to be registered against the land and premises, the whole of the unpaid balance shall immediately become due and payable to the Contractor."

It doesnt matter that you have this listed in your contract. Specificaly, about bankruptcy. Federal law protects certain bankruptcies. An "apointe" is appointed to collect any monies after a bankruptcy. If you (being a contractor) are paid within 90 days of a filed bankruptcy (depending on the chapter) you are considiered "preferrential" and required to pay it back.
It is not wise to take legal advise from any forum. For we (at least myself) are not an attorney.
If you can afford to do business yourself, than you can afford legal advise!