Typically yes. Functionally it does not matter how long they stay in staff after going inactive if they were doing fine before and we don't have reasons to worry about them suddenly abusing their permissions.

Ninjas in particular shouldn't really be of any concern to the vast majority of people, they are not in charge of any particular staff groups nor do they have any actual duties. They're (usually) just there as senior staff members with experience others don't have but they're not expected to be moderating forums / hosting events / etc.