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The breakup of Columbia occurred about 15 minutes after entry interface and the key event in this was the loss of hydraulic pressure due to burn through of all three hydraulic lines.

How much longer did the the entry need to go until the heating started to reduce and eventually cease?

Given that the left wheel well was compromised electronically and hydraulically if not physically, I presume then afterwards there'd have been a pole evacuation. Where would this have occurred if it did?

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The heating had already started to reduce as seen in this graph.

enter image description here

To bailout (at least per the procedure), the Orbiter would have had to be subsonic.

On a nominal entry the Orbiter would have gone subsonic ~26 minutes after EI. On STS-107 the main body breakup was at 969 seconds (~16 minutes after EI). So to make it to bailout, it would have had to hold together ~10 more minutes to make Mach 1, plus a few more for the bailout to happen.

Note that after Mach 1, the Orbiter landed in ~4 minutes.

enter image description here

See Did the astronauts seated on the space shuttle mid-deck have responsibilities during reentry and landing? for the middeck bailout procedures.

Given the low altitude of the Orbiter when Mach 1 was reached, the bailout would have been in the vicinity of the targeted landing site. The procedures did not have the Orbiter turn away or target a specific bailout site. Once Bailout Mode was engaged, the Orbiter would have flown in a straight line.

Sources:

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  • $\begingroup$ Thanks, is there a nominal version of that heating graph? $\endgroup$
    – David Findlay
    Commented Jun 15, 2021 at 1:18
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    $\begingroup$ My speculations as to where the bailout would have occurred: The posited scenario assumes that all parties involved knew (to a decent degree) of the damage and its implications (e.g. in-flight breakup being possible). As such, I'm thinkin' that the deorbit burn would have been done such that the subsequent flight path avoided populated areas. A flight path purely over Pacific Ocean comes to mind... $\endgroup$
    – Digger
    Commented Jun 15, 2021 at 15:27
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    $\begingroup$ @Digger if they were planning for a bailout, that would have the crew bailing out either in Asia or the Pacific ocean. If they wanted to avoid the risk of debris hitting anything on land I'd expect them to aim for the Atlantic ocean so the crew could bail out in the eastern US. That said, I'd think they'd still want to look at the wreckage for whatever they could learn; and would aim for somewhere unpopulated in the southwest, eg White Sands Missile Base. $\endgroup$
    – Dan Is Fiddling By Firelight
    Commented Jun 15, 2021 at 19:18
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    $\begingroup$ @DanIsFiddlingByFirelight, White Sands is only about 35 miles east-to-west -- not much of a target for an out-of-control spacecraft. If you insist on the debris hitting land, I'd aim for central Nevada: there's 400+ miles of just about nothing between Reno and Provo. $\endgroup$
    – Mark
    Commented Jun 15, 2021 at 22:25
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    $\begingroup$ It would have been somewhere over Florida, because the first they knew of a major issue was the loss of pressure in the left main tyres. This would have meant if they made it through reentry a bailout would have to have been called. $\endgroup$
    – David Findlay
    Commented Jun 17, 2021 at 0:59

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