NBC Sports Network getting the NFL on Thursday would not result in the games being on broadcast NBC. NBCSN is cable only. Also, RSNs wouldn't be required and weren't mentioned.
CBS Sports has access to all the Turner channels (TBS, TNT, truTV) if necessary, but they also have CBS Sports Network. If the package is opened up to NBC as well you can easily find enough national HD channels + broadcast to show all the games. Of course some of those networks are not widely carried (CBS SN and NBC SN), but if they got the NFL their carriage would increase dramatically.
Between Fox, NBC, ESPN, and CBS the national channels that have carried sports before and could easily make holes in their schedule on Sundays would be:
Fox Sports 1
Fox Sports 2
CBS Sports Network
NBC Sports Network
Granted, I find such a scenario far fetched, at least this year. Next time around, who knows? What percentage of households have OTA only? What percentage of NFL viewing households have OTA only? Eventually the concept of broadcast vs. cable will go away, even more than it has today. This especially as Fox and NBC build their national sports networks into real competitors for ESPN, and one way to do so will be to get the NFL on those channels.
It's in the NFL's best interests to get it out of a premium package anyway. If they can make as much or even a little less on a cable+broadcast deal instead of NFLST, the increased viewership will mean increased ad revenue for the league. Raw money from DirecTV isn't the only variable in the equation, eyeballs factor in too.