I can sympathise with your frustrations as this has happend to me as well. Notice though, that you meshes have not vanished, they just don’t render. This seems to happen after you scene has reached a certain level of complexity.
The problem seems to stem from the material indices and more importantly, the limit to the number of them. After a radiosity calculation, each mesh is left with a whole bunch of material indices.
What to do:
Seperate each mesh from the big one that results from a radiosity calculation.
In the edit buttons (F9), remove all the indices for each of the new meshes.
For each new mesh, go to the materials buttons (F5) and add (or create) the material you want for it.
As you do this for each mesh, you should see them show up at render time.