Request a new MOBIB card as soon as possible, so that you can use your travel pass again.
Read here how to request a duplicate
Meanwhile, you must be in possession of a valid ticket
Do you board digitally?
Then you travel validly without a MOBIB card. We do recommend buying a new MOBIB card: if you have a dead battery or a bad internet connection, digital boarding is not possible. If you have your MOBIB card in your pocket, you can scan it. Don't have your MOBIB card with you? Then you will have to buy another ticket.
More information about digital boarding