Welcome to the community!
You can certainly decide to return to Fido, however, I'm not sure you'll be able to regain your old plan. Generally, if a plan is no longer currently available on the system, they won't be able to offer it again.
That said, you should note that these forums are community-driven and not intended as a venue for customer services. As such, we do not have access to customer accounts. If you would like to inquire about regaining your old plan if you return, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀