Sorry, but I don't feel the A/P should stay engaged with loss of air data unless it reverts to pure "attitude" hold.
Don't discount the fact that the autopilot is still available with a loss of IAS. There is a selected Pitch Damp mode that the pilot can select to maintain attitude if desired. Options are nice.
I maintain that if AF447 were flying an aircraft with an operable autopilot during a loss of IAS, the airplane would still be flying today and all the folks would be alive. Another nice option.
The question of why such a sophisticated airplane could trip the autopilot with a loss of IAS and abandon the automation dependent crew has yet to be answered.