Because no bids filed by the end of December 2016 to hold the 2019 Westercon, any site on the North American continent west of 104° west longitude, or in Hawaii, is eligible to bid to hold the 2019 Westercon. That includes even the two seated Westercons. There is no restriction prohibiting a seated Westercon from bidding to hold a future Westercon. There are some other restrictions that apply up until the December 31 prior to the election, but if nobody files a bid by December 31, all sites become fair game.
If no bids file by April 15, site selection will proceed with nothing but write-in bids. The deadline for filing bidding papers to be eligible to win the bid as a write-in is the close of site selection balloting at Westercon 70 in Tempe this July. If no bids file bidding papers, or if no filed bid wins the voting, or if None of the Above wins, then the Westercon Business Meeting gets to decide where to hold Westercon two years hence. Again.
Note that while the Westercon Bylaws recommends that Westercon be held over the American Independence Day weekend, this is not required. It is merely a strong suggestion.
If no bids file by April 15, site selection will proceed with nothing but write-in bids. The deadline for filing bidding papers to be eligible to win the bid as a write-in is the close of site selection balloting at Westercon 70 in Tempe this July. If no bids file bidding papers, or if no filed bid wins the voting, or if None of the Above wins, then the Westercon Business Meeting gets to decide where to hold Westercon two years hence. Again.
Note that while the Westercon Bylaws recommends that Westercon be held over the American Independence Day weekend, this is not required. It is merely a strong suggestion.