What are the chances that Bitcoin changes its proof-concept one day?
Chances of a replacement are very low. In fact, this is actually mentioned in the bitcoin community maintained wiki, which seems quite official.

See the "Prohibited Changes" list, where adding an alternative proof algorithm is listed under the "disputed" category. 


  Disputed:
  Adding alternatives to Proof of Work such as Proof of Stake. This could change core bitcoin too much, but with widespread agreement of some sort might be possible.


Note that they talk of adding, not replacing.