Official Blizzard Quote:
At the end of the season, Conquest Points will be converted to Honor Points and any honor above 4000 will be converted to gold at a rate of 35 silver per point. The honor cap will remain at 4000.
All Season 12 items will cost Honor Points (equivalent to their previous Conquest Point cost) when the season ends, with the exception of any items with rating requirements attached. These items will no longer be available for purchase.
The next Arena and Rated Battleground season will begin approximately one week after the current season ends. During the break between seasons, all Rated Battleground and Arena matches will be unavailable. Team and Personal Ratings will be reset when Season 13 begins.