The person will simply be removed from the movies.

That might happen eventually, but recently I've run into lots of errors where I ask the API for the credits for a movie, then I ask for the Person record for each actor or director identified in the credits response, and the software blows up because one of the Person records referenced in the credits response has disappeared. The reference to the Person record should be cleared from the Credits record BEFORE the Person record is deleted, not after.

They are cleared at the same time.

What have certainely happen is that the movie query was already cached at that time.