Update: The parties of the left coalition have publicly reaffirmed their commitment to the coalition, sending a message to Macron that they will not govern under the liberals
not much, the left is not in the majority. This basically means that the president and the PM (nominated by the president according who controls the parliament) the house will probably not agree on anything until the next election. The left coalition can probably form an alliance with Macron's coalition to pass certain legislation which will betray their commitment. Or the President can stall the parliament until the next election and the coalition breaks and eventually loses (IIRC this is what happened last election when France insoumie and the Socialist party "splitted" the vote)