In reply to Gone for good:
I am based in the alps. The reason I noticed your post is that the Taschorn and the Dom are the only Zermatt 4000s that I have so far not done, and was thinking of trying next week. I went to the bivvy hut a few years back with a good forecast - it snowed 30cms at the hut during the night. We bailed down towards Saas (we approached the hut via the Alphubel, which is the easiest way) and a Saas guide in front of us was avalanched...
It's a day to the hut whichever way you go. Then it depends how long you take to do the traverse as to whether you get down to Randa or to the Dom hutte. If you click on the 'sortie' for 9 July 2009 at the bottom of the camptocamp page you'll see that the guys left the bivvy at 4:15 and arrived at the Dom hutte at 15:15, so I imagine they'd have carried on down. I know a very well known British guide who regularly gets mentioned on here who took 16 or 17 hours, so I think conditions are all important. A guided team may take longer and have to stay at the hut. Don't know what the tarif is - you'd have to ask at Zermatt or Saas. It maybe that they'd only do it 1:1, but really I have no idea, sorry.