No, it’ll stay indefinitely, it won’t stay on just for a week.
Sonarr will not unmonitor episodes, it uses profiles to control whether upgrades will be grabbed, if the cutoff is met the monitored flag won’t do anything, but it’s still there.
Nope, it’s not how it works. When you tell Sonarr to monitor future episodes you tell it, as of right this second I want you to monitor all future episodes for this series. Then that’s all it does, it doesn’t store that you wanted to monitor future episodes it just applies it and then forgets about it. This is the same reason that’s not a setting when you edit the series.
That’s most likely due to
Not a feature, a work around to deal with bad data.