My 256GB Samsung SSD from a 2011 13" MBA borked. It didn't quite totally die, but it did bork pretty good 🙂 . It is apprently super rare though, and it took me a while to narrow down the problem to the SSD because the symptoms were so unusual.
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To answer your question about getting the extended applecare; an SSD replacement costs close to $1000 depending on model and timeframe. However, if the computer is in good condition and not too old, Apple offers a flat-rate fix-anything-thats-wrong-with-it which costs $280 -- not much more than extended applecare.
Depending on your habits, technical knowhow, and availability of other insurnace, I don't think applecare is worth it. I come to this considering what it doesn't cover: accidental damage and theft. I'd rather pay $100/yr for a low-deductable property protection policy and deal with filing claims than pay for applecare.