Even if you could give the Blades a long speech about how glorious everything could be without killing Paarthurnax will they tell you No. They will look at you as if you were stupid and then tell you to get out of Sky Haven and not come back.
The Blades want justice and they do not want to serve you as mere sheep. I bet the Blades will rather go back into hiding and disappear completely before they accept defeat.
How is it accepting defeat to throw their lot in with a person who just may prove the be the Talos of the current age? What is it that Delphine tells you? that the blades have been seeking a Dragonborn to give them purpose again. the Blades were originally Dragon hunters. And a Dragonborn to them is the ultimate Dragon hunter. But it seems to me that Talos turned them into something more and with a greater purpose. And if Talos himself, whom the blades revere, knew about Paarthurnax and could have killed him but chose not to, to seek to do what Talos refused to do is to defy Talos, which no true Blade who believes Talos is divine will do openly.
Every step of the way, we are told that our character is walking the path that Talos walked, and yet none of the choices we are given allow us to even take the "I am Talos Reborn!" standpoint. If you are going to tell me that I am walking the same path as Talos, then let me choose to take the mantle of Talos and actively seekd to become the next Dragonborn Emperor. Part of that would be unifying Skyrim, Swaying the blades to my service, crushing the real enemies, and building a new empire by sweeping aside the old one which has abandoned its former principles.
In Morrowind, I was Nerevarine and destiny revolved around me until I defeated Dagoth Ur and was no longer bound to prophesy.
In Oblivion, I was a Kingmaker. The one who made victory against Mehrunes Dagon possible. And though I was qualified by action to take up the mantle of leadership, the game decided to just give me some fancy armor and let me be on my way.
In Skyrim, the game all but hints that I may be Talos Reincarnate... But REFUSES to give me the option to pursue the possibility for myself.
I think it's stupid. If the Blades kick me out of Sky Haven, then I'll come back with Parthurnax and any other Dragobns who might support me after defeating Alduin, shout the doors off the place and tell Esbern and the others, "I'm not here to say let's make a deal. I'm here to say this is the deal!"