How can we answer this, Evan? We need to be a decade or so from now to do so. Plus there are many factors that affect battery life. One of the biggest is calendar aging. My Volt had an 8 year warranty, it's 13+ years old.
Also, rather than the whole battery going bad what we have seen is one or two cells hitting a low voltage. If you could just replace those, the battery would be good. Hence the Ultium platform and it's design to allow a module (several cells) to be replaced.
The warranty is the only thing for sure. Based on the few Volt and Bolt owners who needed a battery replacement under warranty, that's what they got, no charge.