I don't think any station aired that Regis & Kelly episode unless they were an indie or a UPN/WB without a news department...were there any of those affiliates? And by then, especially PT/MT stations would have taken something - CNN, a sister Big 3 network station, etc. with rolling WTC coverage. Actually, FOX was simulcasting Fox News throughout the country especially for those without news departments. UPN took CBS, The WB I believe was taking WPIX and/or CNN as from what I've seen on channel surfing clips from 9/11, especially in the hours after both towers went down.
I wonder what it was like in the studio after Regis signed off saying "We'll all watch it together, OK?" (i.e., WABC coverage). My guess is eventually the directors/producers told the cameras to stop filming, and I'm not sure how long the audience stayed in the studio...would they have left around the end of regular filming (around 10AM) or were they told to get out of dodge ASAP and find a way out? If only we had audience member accounts.
And a technical blurb: Regis & Kelly fed on Galaxy 4R, ch. 24 every morning, in the days of unscrambled analog feeds. They didn't go back on for a week, so my guess is nothing was fed at the regular LIVE time on 9/12-14. Besides, it was all rolling coverage on the Big 3 networks for 2-3 days afterward.
ps: Does anyone know when the Fox network itself went to nationwide coverage? Whether by WNYW or by Fox News? I'm searching the newspapers.com microfilm and find that WFXB-43 Myrtle Beach carried Live with Regis & Kelly...they may have been one of the few that aired this, if the Fox network didn't go to nationwide coverage BEFORE the 2nd plane hit...