Many newbies seem to stutter when they first ask a question here: their question is duplicated.
High-karma contributors have enough privileges to close or delete the question. But every “warden” has his own preference about which question to keep.
My personal habit is to consider the latest one may have been edited and the oldest one is therefore to be put aside.
Unfortunately, we may be two high-karma contributors detecting simultaneously the duplication. When this happens with opposite habits, the net result may simply be deletion of both instances. This is what happened a few minutes ago.
My recommendation is then:
comment both instances with a cross-link making clear which are the duplicates
when this is done and not before, close the oldest question with Duplicate question reason
This is the only way to handle a contradictory personal procedure. Don’t use delete before you know for sure somebody else did not choose to discard the occurrence you thought was left.
check your “left-alive” question has not been closed/deleted by someone else
wait for OP feedback before deleting the extraneous occurrence
Consider a no-response delay of at least 48 hours is safe before taking drastic measures like deletion.