The policy on identification questions is, that they are eligible for deletion when they don't have any upvoted or accepted answers and remained inactive for 4 weeks, as described in the help center and this meta post. Since this policy has recently been updated as described in this meta discussion, there was a recent cleanup session where questions that are thus deletable were acted upon accordingly, yours was one of them.
You might feel like having been robbed and I see that you have put much detail into the question, but such are the rules of this site and they are necessary to tackle the long-term negative impact those inactive identification questions have on the site. If however, you have any new insights or updates to your question that may provide new possibilities for answering, you can add them in and it might get undeleted.
However, I wonder why you haven't been notified of the removal. I thought a deleted question would automatically trigger a user notification. If not, then I see why you were surprised. Thanks for bringing this to notice.