I don't recall if a broken D0 trace will FRAG a box, but I don't think so. The real test would be to put the box back together minus the modchip and see if it boots. No FRAG, should be OK. Even if you can't get any further you can try and weasel your way out by saying you didn't break the box, you were just unable to mod it...
If D0 (or any other trace) needs to be repaired you can always try a trace pen. Here's a link to one manufacturer's web site -
http://www.techspray.com/trace.htm No idea how well it may work on your Xbox, but I know pens like these used to be used to unlock AMD processors for higher overclocking.
There should be alternate D0 points, but may not be as easy to solder to as the first one you chose to work with. You'll want to follow the trace from where you started and look for other points along there that you can tap to. The most accessible are likely going the small holes where the trace taps through the board and continues on the other side. It was one of these points where I had done a top-side solder job for the D0 on my 1.0 board.
-Whoopin'
