How to know what happens to videos that I flag on youtube ?

Bookmark the Video and check it every few days. If its not gone down in a Month, It won't at all.

They will review them when someone flags them and decide if it is inappropriate or not. If it is they will remove it. You will not get any notification that it has been removed they just remove it. If it is not inappropriate according to their rules they leave it on the site. The only way you will know for sure if it is removed is to search it each day