In reply to fifthsunset:
Given you've not had any answers from people who actually know I'll give a bit of a guess... It's been probably three or four years since I was there, so I could well be wrong.
Assuming we're talking about getting down to the midi platforms after topping out the Rebuffat.
I don't think you'll get down with 30m in one from the top. However, from memory I think there are various metal spikes along the line of the abseil which you could use to split the ab into two. If you do that I think you'll be ok.
Having said that I'd rather climb with halves or with a tagline, makes retreating in case of emergency easier and means that you won't have to worry about having enough length for the ab from the top.