Isn't Bitcointalk decentralized forum where everyone has freedom to talk on any subject even against any government?
No it's not and it has never been decentralized forum, but bitcoin is decentralized and that is enough.
If tomorrow Gov declare Bitcoin btc as a money laundering source then we will see Bitcoin word in blacklist and also we will change domain??
That won't happen any time soon, and forum is not directly connected with bitcoin in any way, other than for historic reference.
Governments can make all kinds of things illegal (just look at history), so maybe it's time for people to change the way governments work.