does my cricket paygo account balance last until i use it?

Not necessarily. The funds in your account last until you use them or until your account expires, whichever comes first. You can extend your account expiration date by topping-up your account or by paying your access fee.  Your account expiration date will reset to 60 days from the date of your most recent top-up or the last date your access fee was charged to your account.  In both cases, the new account expiration date will apply to all funds in your account.