Release. The Borough Council shall, by resolution, release or declare in default each performance guarantee. Such performance guarantee shall remain in effect until released by the Borough Council. The amount of the performance guarantee may be reduced by the Borough Council by resolution when portions of the required improvements have been installed and have been inspected and approved by the Borough Engineer, provided, however, that no such reduction shall be approved until the Borough Engineer shall have certified the estimated cost of completing any remaining required improvements. If any improvements have not been installed in accordance with the performance guarantee, the obliger and surety shall be liable thereon to the Borough for the reasonable cost over and above the ten percent cash deposit on the improvements not installed and, upon receipt of the proceeds thereof, the Borough shall install such improvements. The Borough shall also have all other remedies as may be lawfully available.