So long as your account isn't suspended or canceled, and you don't make any rate plan changes, you should be able to continue on the plan you are on in most instances!
Does the plan have an expiration date? Because I'm not sure how long I can use it
Kinda weird one of your questions wasn't answered.
I have been on this plan for over 2 years. When I signed up for this plan I was able to use the app. Several months ago I could not use it anymore. I believe that postpaid plans have access. I call our group "stepchildren". However, I can access my account on the internet, I have a CORPORATE T-Mobile store about 7 miles south of me, and there is 611 if you need account details. From my experience as long as you have at least $3 it's not supposed to expire. Hope that helps!