You don't need to see the bag for it to come back down after a high throw. Even for throws in the 60-80 ft. range you're often not going to see the bag when you're working it in the upper parts of the tree. The answer is that it's done by feel when you can't see the bag or throw weight.

I think working with a throwbag at 200 ft. or more is going to be very rare in tree climbing but when you're throwing into "lower" branches the problems are the same. All the skills that are developed throwing into 50-100 ft. trees are used for super tall trees, it's just more challenging. So the answer to your question "how to do it?" is develop your skills on lower branches and work your way up. It's good to know how throw weights behave in a tree so that when you can't see them you have an idea what to do. There are many tricks and techniques, these are often learned "on the job". Tree Climber's Companion by Jepson has some good throwline advice.
-moss