If past French actions are any guide, not much.
https://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior
https://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior
I mean, they were all released within 18 months. And France is definitely an ally of SA, and the third largest seller of weaponry to SA after US & UK.
Every industrialized country does black ops. France just happened to get caught, once, 35 years ago, and has been paying reparations ever since.
Saying it's "the nation that carries out terror attacks" from this is extremely dishonest, especially when compared to other world powers (hello US).
Most of them aren't targeting unarmed environmentalist boats in a peaceful harbor of an ally.
It was a remarkably stupid op, and I don't think it's at all inappropriate to describe it as a terrorist act.
I think that Macron, being the outspoken politician he is, would probably do something, at the very very least to save face from the far right party who would be all over this.
When has there ever been an instance where the West has punished Saudi Arabia?
Germany for instance had the decency to ban arms exports to Saudi Arabia.