In a fail over situation, such as a small biz scenario with multiple providers, but no BGP, you'll have to deal with rotating prefixes. One alternative would be to NAT to the other provider prefix's during fail over (actually NPt: network prefix translation.) Depending on your firewall / router this may be easier said than done.
Right. NPT is not well supported. NAT66 is out there, but when you think of address space size is totally ridiculous. That said it does solve a bunch of issues.