It appears that the Volt will detect the gasoline going bad (or at least, puts it on a timer and then assumes), and forcibly burn it off roughly once a year. Before doing so, it encourages you to use a bit of gas.
To be honest: this is the first link from a search engine. So its not an issue I've looked into very strongly. Nonetheless, it seems like GM has already figured out a procedure for "stale gas" issues.
It appears that the Volt will detect the gasoline going bad (or at least, puts it on a timer and then assumes), and forcibly burn it off roughly once a year. Before doing so, it encourages you to use a bit of gas.
To be honest: this is the first link from a search engine. So its not an issue I've looked into very strongly. Nonetheless, it seems like GM has already figured out a procedure for "stale gas" issues.
https://forum.quartertothree.com/t/volt-gas-goes-stale/69063
So it seems to be a timer of some sorts, roughly on the order of ~once a year or so.
EDIT: I found a video on youtube showing the process: https://www.youtube.com/watch?v=mEe4Rkg4GfA
The author of the video notes that you can drive the Volt just fine. He just had a camera handy and stay'd in his garage in this case however.