No need to leave, formal explanation in the Away Board is enough. I use to show up after 10 months at a time and that type of inactivity lasted 4-5 years. I got Full Member rank within the first 5 months of my application here and its never been altered within that timeframe because of inactivity.
Also I believe we currently have a member we accepted that has gone inactive immediately after, dont remember his name off my head right now but nevertheless, point is dont worry about it