Yes, 2 internet sources/exits would permit you to survive a internet outage from one provider.
You could them as load balance and as failover (individual or both at same time).
Imagine include a radio, an cable and a 3G internet connection as external for your network and be able to configure who can use what connection. That's a pfSense firewall (but wait there are more...hehehe)
With a RADIO and/or a 3G internet connection as backup you could survive even if a truck run over the light pole ( the most common support for all cables for light and telephony here in Brazil).
Jáder
Jader, you have some valuable information here to share. Would it be possible for you to go to the Wikis and write a Howto about both options your propose:
a) an HW appliance like linksys RV402
b) a SW firewall like pfSense installed on a old HW.
Ass you say, there is more...)
Thanks in advance for any documentation you may produce in the Wikis, then put a link here for reference so that interested people can find this information.
Note: I am moving this topic in General Discussions, what we are talking about is not stricly speaking a contribution for SME.