I don't think Stockholm or Milan will drop out that soon, unless they get a hard no from their governments. There is a real danger of one or both of them failing to get government guarantees by the January deadline though.
The guy from Games Bids has speculated that Salt Lake might step up to host if all three of the Candidate cities drop out before next June.
Also, here's the IOC Feasability Report for the four interested cities that was used to drop Erzurum from the running:
https://stillmed.olympic.org/media/D...ANG-LO-RES.pdf
Despite denials to the contrary, the Turkish bid would have included re-using some venues in Sochi, and very low-capacity venues for other major events.
This is the first I've seen of any concrete plans for the Swedish and Italian bids.
It looks like all three bids have roughly the same amount of new construction required as well as similar levels of renovations to existing venues.
All three mention that the Games will be primarily privately funded, but of course, that's only if you ignore the public money required for security and essential services plus any funding for housing and venue construction/renovations.
If you exclude Whistler, which will only host a small number of events, the Calgary plan is the one with the closest venues. Milan and Cortina are 400km apart, with many venues located between the two cities. The Swedish plan will have the skiing events over 600km away from Stockholm and the sliding events will be in Latvia. The Calgary plan is the only one where a person could potentially watch hockey, skiing, speedskating, curling, and bobsleigh all on consecutive days without a significant amount of travel in between days.