In the end they will die if nothing else in the vape does first. No need to rush that, and hopefully the replacement will be easy and cheap when the time comes.
OF
For the Solo, Arizer will replace it for $95. That's without shipping/customs/etc (thinking about international folk here). So it's almost cheaper to get a new unit entirely.
Or you can do it yourself (and void the warranty): www.vape-nation.com/arizer-solo-battery-replacement-photo-how-to/
Considering that most people have some of the items listed anyway or can borrow them from a friend, the costs should come down to the new battery, which is fair enough.
This is just an example, I hope some of the tinkerers here will take the Ascent apart asap and give us some information about the battery type used (although it should be very close to, if not the same as the Solo's batteries). I think if someone did a short and concise guide for the Ascent, a lot of people would be less hesitant about getting one.