Cell phones are handy but they are more fragile than people may realize. If your battery dies, or you drop your phone and it comes apart, or if you just plain misplace it – or if it's taken away from you, which sometimes happens in an attack - what other option do you have for calling anybody if no landline phone is available?
If the phone line is in order, and you have even a cheap phone plugged into the wall, your home phone may work even if other utilities are disconnected. They aren’t affected by cell phone towers being knocked over or overloaded in times of crisis.
It’s possible that a 911 call center can get a reasonably close fix on your location if you call from a cell phone. They do this be triangulating signal strength from various cell towers in your area. But this is inexact and may only give the police a rough area to canvass, and it relies upon translation into latitude and longitude and then to an area on an actual street map. In contrast to this, in almost every area of the country (including BCS), the moment a call goes through to 911 from a landline phone, the exact address of the location pops up on a screen, without you even having to say anything.
And yes - most phone companies will still allow emergency calls to 911 to go through EVEN IF there is no service contract in effect for that address. You should check with your local provider to be sure about this, but as a redundant means of calling for help, I really can’t see the downside to keeping a landline phone by your bed – especially if you don’t even need to pay for the service to get it.
If you are thinking far enough ahead to be concerned about the very real possibility of your cell phone being missing or failing you in a moment of crisis, then yes, you should look into the landline phone, if only for 911 calls. To not do so would be foolish.