What if someone suddenly loss lot number of reputation, which was enough for him to get new privileges before.
Does this will effect his privileges? Please explain both the cases.
It does not matter how much reputation a user has achieved once, it's only important how much he has at the very moment.
There might be some delays until the reputation changes have their effects on the granted permissions due to caching and that some server tasks are only scheduled hourly or daily, but in general, the current privileges depend on the current reputation score.