I would be surprised if San Francisco moved. San Fran is not that large, but my impression is that the Silicon Valley area (San Jose, etc.) tends to support them well, and there are a lot of people at the south end of the peninsula. San Diego is another large market team.
I would expect the NFL would be trying to move a small market team like Buffalo or Jacksonville.
If the chargers move, san diego still gets to live in san diego, so the still have an advantage over the rest of the country, Padres or not.
Also, don't expect that this stadium gets built. Industry is the crookedest city in all of the US. It's like it's run by aggy. All the city council is related, they all take hundreds of thousands of dollars from city contracts, it's a clusterfuck of epic proportions. Only 500 or so people live in this city, the rest is all factories and other businesses.
They only need 3/4ths of the owners to agree. Owners don't stand in the way of other owners, and they would need to swing 8 votes. The only ones who would vote against it are the Rams (voting against Raiders/Chargers) and the Raider/Charger combined camp voting against the Rams.
It honestly looks like a done deal. Kroenke "broke ground" on his Inglewood property, but only as a ploy while he builds more commercial stuff there instead of a $1.85 billion dollar stadium. The Rams are going to be stuck in St. Louis and the citizens of the city (which isn't that big, by the way) are going to be on the **** end of a $400 million dollar bill for 1/3 of the final cost.