I very much doubt that it will "kill" lithium. There are a...

I very much doubt that it will "kill" lithium. There are a number of factors as to why. One is the simple fact of where they sit on the periodic table. Lithium has an atomic weight of almost 7, whereas Sodium has one of almost 23. These are immutable. If you look a bit deeper into the chemistry of both batteries then you may find some interesting things. One thing when I looked into it some time ago was the energy density of these batteries. Whilst the sodium batteries are cheaper since Sodium is extremely abundant, hence the appeal, they also have a lower energy density. This has an effect upon where they can be used. It's unlikely they will be used in large energy storage nor in large transport (think trucks, trains, mining equipment). However, they will most likely find a niche in small vehicles (bikes, and smaller cars).

Only time will tell, of course, but as it stands there will be multiple applications for many of the battery chemistry types. As with most things it's not a one-size-fits-all approach.