@Ange2 There are lots of options. You can get a mobile hotspot (which DOES work if your cable internet goes out). Some routers support a SIM card, and will fail over to the mobile network if the land-line goes down. Other routers allow you to plug in your cell phone via USB to use as a backup.
Of course, if you're home, you can just use your phone's hotspot in an emergency. Most phones support 6-10 or so connections which should be plenty for you and your guest on an emergency basis.