Since tex.se.com has been launched does that mean
latex is off topic on stackoverflow.com?
It depends on the question.
If the question can legitimately belong to one site (say it is a latex programming question), then it is not off-topic and can remain on it, even if there is a more specialized site for the question.
If, however, it is about some aspect that is not covered by a site (say the question is about typography in tex, asked on Stack Overflow), it is off-topic by nature and should be migrated.