In the Promesse de Vente we usually request that the purchase be subject to a conditional clause (“clause suspensive”) which lays out the minimum terms of a loan that you are willing to accept to purchase the property. Ordinarily you will have 45 days from the signing of the preliminary sales agreement to secure that financing. If you are unable to do so (in the preliminary sales agreement you obligate yourself to try) the agreement is automatically cancelled.
You are therefore excused from purchasing the property and your 10% deposit is refunded.
Not surprisingly, sellers are not too keen on this clause and it can be a bargaining mechanism if it does not appear in the Promesse de Vente for example if you are buying but not financing the purchase with a loan, if you are financing with a mortgage obtained outside of France (which this rule does not cover) or you agree to drop the clause to obtain a better price in negotiations over the overall price of the property, which can be advantageous.