dual-homed BGP

Hi! We've an FTG E 200 ver 5.6 and several web servers in our data center. In order to improve the service We want to deploy a dual-homed , fail over solution. ( 2 ISP) I read this article http://help.fortinet.com/...ple.htm?Highlight=bgp, that is vey clear ,but there is also a way to connect to 2 ISP using sd-wan configuration. My question : which is the better way to achive tha goal. Because SD-WAN is more simple but I don't undestand how the web server will be accessed when the main link fall.

TNX