What kind of battery is used in your cell phone? Any cordless tools? What kind of batteries do they use? 
Lithium is light and chemically reactive. I think it will be here for a while yet. As the liquid electrolyte is reduced and maybe eliminated altogether, the thermal runaway tendency is also reduced. As the tendency to catch fire is reduced, the amount of cobalt required is also reduced. Lithium continues to get cheaper and more widely available so I think it will be with us for some time.