CyberBob of the Pax Nimbus pointed out to us that Massa of the Halo Network posted the answer to a question he asked Allen Turner of Bungie. Massa asked if it was possible to fall off the ring. Turner responded:

This is easily the strangest Halo question I have had. I have to say I don't know what will be seen at the edges. However in a real world situation where such a thing existed you probably would never come across an edge due to your size vs the relative size of the Halo. There are also the much of the same gravitic/rotational effects that keep you from jumping off of the earth. Use your imagination and a little bit of science.

So while we might still be able to go roof-surfing, it looks like we might not be able to jump off the edge. Sorry, guys.

ALERT: While Turner's answer is posted in English, the rest of the site is in German.