Now the condition of the above-written Guarantee is such that if the Contractor shall duly perform and observe all the terms, provisions, conditions and stipulations of the said Contract on the Contractors part to be performed and observed according to the true purport, intent and meaning thereof, or if on default by the Contractor, the Guarantor shall satisfy and discharge the damages sustained by the Employer thereby up to the amount of the above-written Guarantee, then this obligation shall be null and void, but otherwise it shall be and remain in full force and effect but no alteration in terms of the said Contract or in the extent or nature of the Works to be executed, completed and defects therein remedied thereunder and no allowance of time by the Employer or the Engineer under the said contract nor any forbearance or forgiveness in or in respect of any matter or thing concerning the said Contract on the part of the Employer or the said Engineer shall in any way release the Guarantor from any liability under the above- written Guarantee. Provided always that the above obligation of Guarantor to satisfy and discharge the damages sustained by the Employer shall arise only.