if you break the driveshaft or diff, it would still run, but will have a very disturbing "clunking" sound.. had the same problem with my friends S2k..
so cliff notes of this problem:
*driving 100 miles @ 70 mph cruising
*5th gear suddenly popped out and couldnt get it into to ANY gear since
*clutch line and pedal are firm and checked no fluid leak
*could get into gear @ idle but doesnt go nowhere
*Car doesnt go into gear when car is off
You might want to clarify the 2 bolded red lettering... and maybe write a cliff notes of your own for everyone to understand. apparently im gettin confuse myself..=/