If bitcoin becomes centralized, then a 14 year old kid which read books about bitcoin in his hostel room, and create something more powerful than bitcoin.. Since it is open sourced, you will not really need to worry about it.
Nope I think bitcoin will be decentralized anytime. the government with their power will not be able to turn bitcoin into a whole centralization. the bitcoin internal system can not be changed from the outside. but do you know decentralization starts to disappear when the exchange begins to ask for verification id?