The City Commission shall either approve, partially approve or reject the improvements on the basis of the report of the City Engineer and shall notify the obligor, in writing, by certified mail, of the contents of said report and the action of said approving authority with relation thereto not later than 65 days after receipt of the notice from the obligor of the completion of the improvements. Where partial approval is granted, the obligor shall be released from all liability pursuant to its performance guaranty, except for that portion adequately sufficient to secure provision of the improvements not yet approved, provided that 30% of the amount of the performance guaranty posted may be retained to ensure completion of all improvements. Failure of the governing body to send or provide such notification to the obligor within 65 days shall be deemed to constitute approval of the improvements, and the obligor and surety, if any, shall be released from all liability pursuant to such performance guaranty for such improvements.