Your spot on the server is saved, but not in the queue. After you leave, you can come back without queueing — but only within 5 minutes. Longer than that — you will have to queue again.
The number of slots on each server is tuned deliberately — it keeps the balance between performance and population, so we are not planning to expand them. Want to spend less time in the queue — get any privilege on modded servers or "Queue skip" on Vanilla/Classic in the store.
