I believe we have (at least) the following cases to consider:
License
First publication
Uploaded to Wikimedia
What happens?
GFDL 1.2 (or earlier) only
anywhere
any time
stays GFDL 1.2 (or earlier) only no matter what.
includes GFDL 1.3
on a Wikimedia project
before June 15, 2009
becomes multilicensed with CC-BY-SA 3.0.
June 15 – August 1, 2009
not sure... the GFDL allows multilicensing here too, but the Foundation resolution isn't quite clear about what should happen in this case. Ideally, this case should not arise, but it practice it probably will, either because other projects are lazy about updating their license selectors or because users choose such a license manually.
August 1, 2009 or later
stays GFDL, since the relicensing clause will have expired.
outside Wikimedia
before November 1, 2008
becomes multilicensed with CC-BY-SA 3.0.
November 1, 2008 or later
stays GFDL.
Where "GFDL 1.3" includes "GFDL 1.2 or later" or any variations thereof. Of course, all of this is irrelevant for works already multilicensed with CC-BY-SA (version 2.0 or later) or with any non-ShareAlike license.