Had the space shuttle ever launched out of Vandenberg AFB, its primary transoceanic abort landing (TAL) site would have been Mataveri International Airport (SCIP) on Rapa Nui (Easter Island; Isla de Pascua), a selection forced by the lack of other usable islands in far eastern Polynesia.
Unfortunately, Mataveri is also the most remote airport in the world, 2602 kilometers from the nearest other airport, Totegegie Airport (NTGJ) in extreme southeastern French Polynesia,1 and the Shuttle Carrier Aircraft has a range of only 1850 kilometers when carrying the shuttle.
Would the SCA have been modified to give it extra range for retrieving the shuttle from a Mataveri TAL, would the shuttle have returned by sea, would the shuttle have been disassembled at Mataveri and flown out in one or more ordinary cargo planes, or would something else have happened?
1 - Upon further examination, it appears that there isn't even any land outside the Rapa Nui group that's within mated-SCA range of Mataveri - even Henderson Island in the Pitcairn group, the closest other land to Mataveri, is still just out of range, at ~1912 kilometers. (It also happens to be uninhabited and have no airport, but, even if NASA had had an airport built on Henderson, it still wouldn't have been close enough.)