Then neither is going to move.
The Rams are gone. Unless someone in LA manages to block Kroenke's project, that stadium appears to be a guarantee; they've already broken ground on the rest of the complex. Mike Florio has already talked a bit about how Kroenke very likely would go full Al Davis if the league made an attempt to block him.
They won't let three teams move to the city. If one of the two other stadium plans is still considered cost-effective after the Hollywood Park project, maybe the Raiders or Chargers can partner up. But most likely they will end up a tenant, and the other will either take whatever they can get from Oakland/San Diego or move elsewhere (probably St. Louis, if the state of Missouri does what they are saying and builds their planned stadium no matter what).
I think the NFL would rather do something more along the lines of a team swap and leave the Rams in St. Louis, provided they approve the financing for the proposed new stadium. The last the the league probably wants right now is for a team to bolt a city that was ready to build them a brand new palace. So....since he's got his own stadium project well off the ground, maybe have Kroenke swap teams with either Spanos or (more likely) Mark Davis. Then Kroenke moves his new team into the Hollywood Park stadium, Spanos or Davis gets the Rams in their new St. Louis stadium, and whoever the third team is can either work something out with one of the other LA options or with their current city.
It's somewhat similar to what MLB did with the Red Sox/Marlins/Expos years ago, only this time the league doesn't have to take ownership of a team (unless Al Davis' widow dies before anything can happen and Mark Davis is forced to sell the Raiders, then all bets are off).