If you see the "Completed" status in the subscriber list, here's what it means:
The subscriber has reached the end of the sequence, there are no more messages to send.
The Quick Start Campaign was deactivated for more than 14 days, and then later resumed. We removed these old subscribers from the sequence to avoid embarrassing you with old messages. This only applies to Step Sequences triggered by Events.
It should be noted that if your date sequence is marked to "Run Annually," then the subscriber will never be marked as Completed.
If a subscriber was removed from a sequence, they are marked as "Removed."