Is it possible for someone who has a 200 level ticket, to be able to go down to get autographs and then return to their seat ?

Sure tell the event person what you are doing they will escort you there and back

Not likely. They have ushers checking tickets and won't let anyone go anywhere they're not allowed

You won't be able to go on the floor, but you can go to the bottom of the section and stand for an autograph.

Only if the usher will allow you in the section.

Basketball fans

Am not sure

It's impossible.