I'm still following the story - but here are the developing news reports. Summary: Tariq Aziz has tried to escape through the north, there were unconfirmed rumors he was shot dead, but it is still unknown.
Albawba.com: Unconfirmed opposition reports: Tareq Aziz shot dead
Sky News: Tariq Aziz: Defection rumours
The Independent: Mystery surrounds fate of Saddam's deputy
Canoe News - Iraq's deputy PM defects?
It looks like the US is denying it - stay tuned to Google News for more.
UPDATE: Iraq denies it and so do the Kurds. Tariq Aziz was still there on Tuesday:
Aziz was seen in Iraqi television coverage of Tuesday's cabinet meeting with President Saddam Hussein and senior diplomatic sources in Baghdad said they had heard nothing to indicate the rumours circulating abroad had any foundation.
But there are many Iraqis fleeing north...
FINAL UPDATE False rumor. Tariq Aziz appeared live on television specifically to dispel the rumor.