Best case scenario would be that ECOWAS gets their asses handed to them, and maybe that leads in some anti western coups within ECOWAS. This is basically the last colonial stronghold that the west has in Africa. If ECOWAS ends up collapsing, then western position will be untenable. Given that African Union is against intervention and Niger has support from the neighbours, I don't think ECOWAS is going to have an easy time here. There also seems to be a lot of disagreement within ECOWAS regarding this because it's pretty clear that the west is pushing them into it.