Football is king in almost every city that has professional football. I have lived in the Detroit area all of my life and no team gets the kind of hype (good or bad) as the Lions, and we have the Red Wings (arguably the most consistent and best franchise in sports for the last 25 years.) The Tigers and Pistons, both who have won more titles than the Lions have won playoff games in the last 50 years (Pistons 3 Tigers 2, Lions 1).
If you took the Saints from New Orleans I have a feeling they would burn that city down, it would make Katrina look like an average rain storm. There really is nothing else to say about the passion that city has for that team.
As far as the Vikings it would be just as bad, I had relatives that have season tickets to the Vikings and they drove the 14 hours + 5 more due to the weather when the Metrodome roof caved in and they moved the game to Ford Field, not to mention the realigning that would have to be done with the Vikings moving that far west. (It might be as simple as switching St. Louis and Minnesota but I don't know). Lastly Minnesota has one NFL franchise, how many NFL franchises does California need. It already has the Chargers, 49ers, and the Raiders.