Well, in my experience... when bike rallys go on busy roads, they do not shut the roads down. Instead, they have cops directing traffic at the intersections, but otherwise you are on the road with cars.

A "no drop" ride means that no one gets dropped from the pack. The ride goes as fast as the slowest rider... or there is someone who sweeps the back of the ride to keep an eye on the slower people. From my experience, bike rallies do not offer no drop options, but they do have SAG (support rides) wagons to pick you up and drive you to the finish if you can't make it on your own.

Bike rallies... are fun. Go for it!