18447 is closed and locked, so it can't be answered, commented upon, or edited. It also can't be reopened, at least not by the normal community voting process.
All of the comments previously left on 18447, at least some of which look valuable to me, are now attached to 18453, and are invisible to most users.
18447 has a link directing users to where they can get answers, but for most users, this will be a broken link.
This situation leads me to the following specific and general questions:
What can/should we do about 18447? Un-merge it somehow, reopen it, and unlock it? Reinstate the comments that got sent to 18453? Undelete 18453 and leave the merge in place? Delete 18447 and wash our hands of the situation?
Should the system be fixed to prevent this sort of situation from coming up? Should merge targets be protected from deletion, or possibly auto-delete their merge sources if they are deleted? Should mods get a "de-merge" button to allow for smooth reversal of an entire merge, or perhaps a "reverse merge" button that points the merge in the other direction and moves comments and answers to the new target?