Posts and threads are only removed if they violate the code of conduct (or the EULA/Terms of Use Agreement), or if they are quoting or responding to another post which is removed for violating the rules. If you think a post was removed by a moderator in error (that the post did not violate the rules, wasn't quoting or responding to a post that was violating the rules, etc), you should contact a moderator to raise your concerns, or contact support with a support ticket.