You should also look into software escrow. Large corporations often require this of smaller vendors delivering enterprise solutions (SaaS or otherwise).

Your agreement is great in spirit, but I believe the moment your company ceases to exist your customers will lose legal recourse over your commitments. IANAL, but I would assume that includes this open source guarantee. That's why there are a number of third party companies who provide escrow services. Iron Mountain is an example:

http://www.ironmountain.com/Services/Technology-Escrow-Servi...

Edit: Fixed formatting, wording.