D3 always had his ups and downs. Lots of people stoped playing for what ever reason(s) and others picked it up (again). The end of THUD is most likely not the end of D3. How ever i guess that some/many/a lot of those who play D3 more serious might quit. Still we have to keep in mind that Blizzard never realy cared much about the 1% on top of the foodchain. They always cared about those who play more casual. Most of the recent changes aimed towards these players which is totaly fine imo. They learned their lesson back in D3V when Inferno was clearly over the top. The majority of their Playerbase dont play for several hours each and every day. And those people usualy dont feel the need to use either THUD or a Bot. They just enjoy slaying Monster every now and then.
So imo both sides of the fence are right: Yes D3 will lose part of the competive scene. Yet the playerbase is not shrinking in such a drastic way.