Answered question
Once you apply an upgrade, do they expire or are they there forever as long as you stay with Fizz?
Is not correct
Upgrades: Each time you reach a new Level, you unlock a new Upgrade — a unique and permanent privilege — for example, unlimited calling, additional Data. Every Upgrade is valid for two years starting from the date you receive it, whether you apply it to your plan or not.
Other answers
it stays forever but it has an expiration if you don't apply it after 2 years
2 years is not the same as permanent. It seems like even Fizz isn't sure.
I will stick with the 2 years