In the end all that matters is does Nigeria want to fight this war or not. They're the ones that'll be paying for it in blood and treasure. France is a sidenote. They're not going to die over this.
Nigeria is, by far, the biggest country in ECOWAS. If ECOWAS militarily intervenes in Niger, it'll be Nigeria that is able to supply the bulk of the money, equipment, and manpower
Because you don't just have a coup after having a stroke of insight from a night of binge drinking?
It's a movement led military units that have deep political and intelligence connections. They know a lot of things that aren't going to be admitted by the West.
So far a leader of a military group, which has just overthrown a democratic elected leader, which cooperates with the Wagner group to secure their might, claims that France is doing that.
I would put a big question mark behind that claim and wait for reliable sources.
France used to control Niger the same way that Russia controlled Ukraine. Now that Niger and Ukraine are independent countries, I'm sure the response to both will be consistent.