I will be flying both internationally and domestically quite often.  Will I be required to have the REAL ID?
Yes.  If you have a standard license you will not be allowed to board domestic flights beginning in October unless you have a passport.
If I had a REAL ID, but it has been misplaced, can I replace it by mail?
Yes, indeed, you can.  If you already have an Enhanced or REAL ID you can replace by mail and your document type will stay the same.