I think Edouard Philippe could go even if Macron is going. He is ambiguous in his words.
Of course he is ambiguous. You leave ambiguity only at your own risks. There is nothing to win now taking a stand.
the more he stays shady the more we will talk about him, he will be able to count his people, see how people react, while keeping his options open.
But he won’t go if Macron goes. Not enough political space, and him vs Macron everyone loses.