This thread is old but I think it is still useful for many.
My 2007 Civic Hybrid started failing about 100K. The signs of failing hybrid battery pack are fast discharging and charging by the battery capacity indicator. You will also experience loss of power and drop in gas mileage. By that time, the IMA warranty had already expired. But after some persuasion, Honda agreed to replace the battery pack with a refurbished one for a mere $250 “insurance” fee. Honda knew that they had some bugs in their battery management software, but they also played nicely.
Fast forward 4 years, now my Civic has put on 50K miles on the refurbished battery pack. It started to show aging again. Now, there are plenty of refurbished battery pack offered by 3rd vendors for a little over $1000 with trade in. I consider that cost acceptable.