To my knowledge, none of the previous respondents have written the check for a replacement pack. I have, and a new (not reman) pack from Tesla. So my comments comes from that perspective.
First, whether a pack fails is a gamble. There are some things you can see with an app like Scan My Tesla that can help determine a pack's health. However, a truer test is CAC imbalance and currently on more sophisticated testing equipment than Scan My Tesla.
As
@Recell has stated "There can be a number of factors that may cause a pack to fail, but a well-balanced pack, even an older one, with a (CAC) delta less than 2% across each of the modules will continue to deliver years of safe, reliable power."
In my case, I got the BMS_u029 alert requiring out of warranty pack replacement 3 days after I purchased my 2012 P85. However, I'm sure the majority of early Model S owners report their original packs are doing just fine.
Agree with
@GHammer that if you don't have money set aside ($10k-$20k) for repairs, then you should look for another car. I realize the current market is making these older Model S's affordable (that originally were over $100k new) but they are expensive cars to maintain.
If you have any further concerns, suggest you join this
Facebook Group