Crocs replaces both straps and rivets free of charge. I had a rivet break once, used the website contact form to request (what I thought was) 1 rivet and had a little ziplock baggie of about 8 replacement rivets in my mailbox within a week. If the strap is intact and has just come free of the rivet, that's all you need. If the actual rubber strap has broken (either the strap or the little hole around the rivet), you'll need a strap replacement.
From the Crocs website:
Will Crocs, Inc. replace a broken rivet?
Yes! Click here to request rivets! You will need to register for our website if you are not already. We will send them to you at no charge.
Will Crocs, Inc. replace a broken strap?
Yes! Click here to request a strap. Please give us the size, color and model of the shoe. Include your shipping address and we’ll ship you a new strap at no charge.
Rivet specific request link:
https://shop.crocs.com/signin.aspx?returnURL=RivetOrder.aspx
For straps, you use the general contact form and put your information (size, color, etc) in the comments box:
http://www.crocs.com/contact_us/
DH can't complain about that, right?
