I came to this a bit late, but it's absolutely fascinating to me and now that I've read it I'm going to spit out some rambling thoughts on the subject from a setting perspective. Apologies in advance.
There are two main variables, to my thinking: a) how difficult/unusual is it to make a pact, and b) how many patrons can a warlock make a pact with? If pacts are difficult and rare, warlocks are strange aberrations, and the question of how many patrons there are becomes less important to most people. Any warlock is a scary or miraculous thing with powers the average person doesn't understand, granted by forces they don't understand. If pacts are easy to make, though, you're going to see a lot of warlocks. The demand for magic in a D&D world hasn't gone down, just the number of options for getting it. And then the patron "economy," so to speak, gets a lot more important, because any fighting force is going to have the choice of either going without magic or being influenced by a patron. That means pact magic runs through a lot of adventuring parties, but it also means it runs through the city guard. And the army. Every army.
So, how many patrons are there, and how well do they work together? If there are a lot of options for patrons, people will probably favor the most benign options. The effect of patrons on society will be relatively low, both because people make pacts with the least demanding patrons they can find and because society doesn't need to depend on any one patron for survival. If there are only a few patrons, and they don't get along, you're probably going to have something like Stalker0 said, a hot or cold war between... uh... patron-ocracies. There might be kings or parliaments that are independent on paper, but in practice they're still going to be dependent on one of the patrons.
What if pactmaking is fairly easy, there's a moderate number of possible patrons in the known universe, and they get along moderately well? Then each patron probably has considerable power over society, but not absolute power. Mortal authorities will try to keep any one patron from becoming ascendant in their country, for their own safety: if the prime minister sees that his army has a lot of warlocks from Patron A in it, he's probably going to encourage his soldiers to make pacts with Patron B or Patron C. When patrons go to war, it takes place all across the world at once: patrons have agents in multiple countries, and a warlock's loyalty to their patron is higher than their loyalty to their nation if they want to keep being a warlock. Mortal authorities will do what they can to contain or suppress battles between warlocks, of course, but their ability to do so will be limited by their dependence on their only sources of magic. I think this would be an interesting world to play a game in, but it should probably be run by somebody with more cyberpunk experience than me.