You will not receive a notification when your request is denied.
To see whether a decision on your flag was taken already or whether it is still pending you check your flag history (see A way to view your flags)
Generally, a request for migration being a flag will be handled by the site's moderators as they see fit and when they have the time to do so.
A common practice in cases of doubt is that a moderator of the source site asks a moderator on the target site about the request.
Another thing that is likely to happen is that some moderators skip the flag to leave it to a moderator whose field of expertise is closer to the question.
To sum it up, either your flag was already handled negatively and you did not notice or the request is still pending as it can take some time to arrive at a decision for the reasons outlined above.