You’re not completely stuck if you can’t update to 10.3.4 before November 3rd, but you will have to backup and restore to a computer if you intend to move to the newer software. Other devices like the fourth-generation iPad are also affected, but they’re only expected to lose GPS functionality.
There won’t be too many people affected by this. Apple says that 9 percent of all iOS device users are running software earlier than iOS 12 as of October 15th, and many of those are using newer hardware (the percentage shrinks to 7 percent when you limit the data to devices four years old or newer). Still, it’s not often that a company has to urge people to update a device seven years after it launched.