In addition to @Cody@Cody's excellent answer to the specific post in question, I thought I'd take a stab at answering the broader question you ask; what to do if you disagree with a moderators decision to lock/close/merge/destroy/laugh at/etc. something.
Moderators are people too, and can make mistakes, but I doubt anyone is firing off deletion actions in the dark, as such there is usually a strong evidence in the post that the action is merited, and correct.
In other words, if you strongly feel the decision to [insert actual action here] is wrong, you can flag the post for re-evaluation, or ask on meta (as you did.)
However, and here's the deal many leave out, be prepared to defend the post and explain why you feel the action taken was wrong.
Merely saying "This should not have been deleted" is not going to change anything at all, and will only serve to lower your flag weight.
Note that this is not in relation the specific question you asked about. It did, however, seem like you were asking two distinct questions:
- What to do if I disagree with a moderators decision (and evidence points to me being right)?
- What about this particular post?