If you did not make any phone call or chargeable text message from your swiss Lebara line (once within 6 month period) you number will be automatically deactivate from the system.
Unfortunately Lebara should not be able to reactivate this number but if it still on your balance more than CHF20 (CHF20 is the price for a balance transfer from old expired number to a new Lebara existing number) Lebara can transfer your old balance to a new Lebara number (this new number needs to be registred under the same name than the expired account, I mean yours, if not the transaction will be impossible).
Ex 1 : Old expired number 076*****5 with CHF 40 balance left.
You can take the money back to your new existing Lebara number 076*****6
at least : CHF20.
Ex 2 : Old expired number 076*****5 with CHF15 blance left.
You will lost this money as the balance was under CHF20, so, you cannot cover the fee for the transaction.
I hope this explaination will help you
Have a nice evening.