For reference I have a 2015 LEAF SV with 45,000 miles, 75 mile range. 10 bars (12 max).
To your question will it lose range? Yes about 2% or 3% year. I tacked mine and it has slowed a lot since I started charging only to 70%. Or course that lowers my range 55 miles. Then I try and not go below 15 mi. My practical range is 40 miles. The limits are voluntary. I have been holding onto 75 mi range for almost a year. But doing the math 25%/9 yrs = 2.7% / year loss in range.
To your question of sudden death of battery? Yes a single cell can fail and drag the whole pack down drastically. It can happen. There is an App called Leaf Spy. It plugs into the data port under your dash called OBD2. It uses a Blue Tooth dongle and the App on your smart phone to look at your battery and show each cells voltage. You want them more or less even. This can't fix or even out the cells only show you if a cell is going bad. They will never be all equal.
My typical errand is about 8 to 10 miles. If I combine a trip 15-20 miles tops. So my range works for me. I just have to charge way more than I use to. I started with near 95 to 100 mi range (bought car used in 2017), It had 12 bars and 23,000 miles. After about 6 mo it dropped to 11 bars. I am now at 10 bars after 7 yrs. I estimate I have another 5 to 8 yrs before I either replace battery (with a used one), sell it and get another car. This is a second car for me, single driver. I am tired of paying registration tax and insurance.
