By introducing the concept of multi-homing, it is necessary that you have your own public autonomous system number, that is provided that you are multi-homing with two different Internet service providers. If you are multi-homing with the same internet service provider, it is not uncommon to see a service provider extend their, system to you.
If the objective is to have failover, that is you're advertising the same block (subnet) at each site with metrics applied systematically that allow for failover, then yes, it is necessary that they have some connection between them. iBGP would allow the two routers the ability to communicate and failover one for the other in regards to the WAN connection. The speed of the link doesn't matter. It all boils down to if the company wants to stay online in the event of a network outage at one location caused by an equipment failure or the loss of a link at a site.
