I have presumed the west away from the incident as i guess its too dangerous heading towards the wreckage.
JonF,
There is a proper formula for working out how to arrange for departures towards a temporary obstruction. Normally when Ops Managers run a paper exercise for training purposes such obstructions are given somewhere in the middle of the runway, but this particular accident was interesting as it was right at one end. Basically, one measures the height of the obstruction (this a/c was a bit lower than otherwise due to the undercarriage collapse) and take a 1:60 slope, then add 90M and some other bits and pieces (in basic terms). One then measures from the beginning of the take-off roll to this point and declares it as the Take-Off Distance Available (TODA). With Heathrow's long runways, this distance might have been useful enough for quite a few types. Fortunately the wind continued to favour departures away from the obstruction. The main consideration in this latter case is blast for those working at the scene. Departures were I believe from the intersection of 27L with what used to be 23 (Left if you go back that far) Runway 23 has been closed for a couple of years, now and might have been useful in this case, if the SW wind had picked up a bit more.
If the 1:60 slope is too restricting and you've not the luxury of 2 runways to play with, then you can always reduce the height of the obstruction, i.e. cut the tail off the aeroplane that's in the way. This was done a couple of times at the old Hong Kong aerodrome at Kai Tak.
In Heathrow's case with a wind blowing from the East, the sensible way of dealing with the obstruction would have been to declare a reduced landing distance towards the obstruction (there's another formula for working out what distance to declare)and departed from 09L. However, there is something called the Cranford Agreement (though I'm told that no-one can find the piece of paper it was written on any more) which severely restricts 09L departures due noise over Cranford, which is very close.
Cheers,
TheOddOne