"return to civilian rule" means that Niger's military cedes formal power back to national political institutions with non-military leaders.

Currently, the presidency's incumbant, Mohamed Bazoum, appears to be detained in the presidential palace, while the National Assembly is suspended.

As examples, this question resolves Yes unambiguously if (a) President Bazoum is restored to power peacefully, (b) elections are held that establish a new civilian government without Mohamed Bazoum, or (c) a foreign military intervention topples to coup leaders and installs a new non-military government, or restores the previous government.

If it's unclear if civilian rule has been restored, I will use reasonable judgement. For example, if the military restores the legislature and the presidency, but the coup leaders go unpunished and remain an influential actor that still pull a lot of strings, I would count that as a Yes. By contrast, if a coup leader declared themself President, but also restored the National Assembly, this would count as a No, since a significant part of formal power (the presidency) remains in the hands of the military.