Your number will be recycled if you don't buy a membership for 13 months in a row.
See here:
https://48.ie/legal/terms-and-conditions#7
"7.3 Where the 48 Services are suspended because you have chosen not to purchase top up credit or make a chargeable use in respect of your Account for a period of 6 months, we will remove any credit on your Account after a further 2 months and credit will not be recoverable. Your service will then remain suspended for a further 5 months and can be reconnected at any time during this period. When the suspension period ends your service will be disconnected, this agreement will end and your number will be immediately lost."
Hope this helps.
