As long as you have a good and a high quality post, it is very impossible to be deleted, although these are some problems now that mostly of my friends says that they found of rapid deletion of post, but if a person who actively posting time to time there's no problem on that such kind of issue. All we need to do also in opposite on that issue are being active on posting, not only the minimum required post but we must also provide extra post by monitoring time to time or on any vacant time. But deleting of post is not actually a big issue, the worse is the merit system, because all of us are impossible to improve our rank even we are very active on accessing and posting.