I expect an LCD to have a lifetime in the order of many years, possibly decades. A quick Google search gives me numbers of 50-100k hours on full contrast, so up to 11 years.
The LED for the back light will typically last for about 50k hours (almost 6 years) on full brightness (20 mA). Lower that current (4-5 mA is usually enough) and lifetime should go up a lot, and you should easily get 10 years out of your back light.
So that shouldn't be a real issue.