Why do people want to fight them?, with Negaduck, Judge Doom and possibly Syndrome coming back, shouldn't Doof be gathering vassals, minions and allies, I mean its possible due to the two villains quirkiness that fighting them and winning would make it easier to recruit them later on, but still shouldn't diplomacy be attempted first?
[X] Attempt communications (These two seem to have more of a quarrel with each other than anything else, you're just caught in the middle. Maybe one of them would see reason, leave town… or even enter your employ?)
-[x] With Lizzie
-[x] With Stanley
As for Sinatron, why oppose him in the first place, first of all
A. Its better for him to be king, than Syndrome reclaiming his power
B. It seems that like, Doof, he is interested only in taking over Las Vegas not the world.
C. He is one of the first sentient robot and AI ever created, he could be a way for Doof to diplomance other AI, sentient robots and machines.
D. He seems ignorant of the masquerad, idiotic than malevolent, if Doof and Rufus were to actually talk to him about why its a bad idea to declare Las Vegas as separate from America, he will likely understand, what with him being low on resources, low on allies.
E. He should at least be given the benefit of the doubt like Doof, if he wants to try his hand at taking over Las Vegas, and turning the place into a cape sanctuary.
F. With other threats out there, it pays to have as many allies to put out fires.
G. It may not be a good idea to snub him and leave him to his own devices, since with the lack of resources and allies, he may be at the mercy of Syndrome's wrath.
H. If Sinatron is sufficiently strong, he could keep Syndrome busy, if Syndrome manages to escape giving valuable time for Doof, Shego to build up their powerbase.
There is a way for Doof to give the chip to Sinatron while, keeping the FBI appeased, Shego interested in a alliance, and Sinatron a obstacle that can give Syndrome a headache at worst.
First step is to clear up the misunderstanding, we have to make it clear that Doof panicked and ran away without giving up the chip due, to not wanting to draw Syndrome's attention and wrath ( in otherwords making it publicly known that Doof dealt a heavy blow to Syndrome), and Sinatron antagonizing the Representatives of the government by declaring Las Vegas separate from the state.
Second step make it clear that Sinatron has to follow the rules of the masquerade involving the government, explain to him the concept of masquerade, how Sinatron due to his volatile position can't afford to antagonize or make needless enemies when he could be making allies.
Third step convince Rufus the FBI agent that Sinatron is a better altenative to Syndrome, Syndrome really if he could, he would commit genocide on capes at worst or at best would heavily discriminate against them. thus making Sinatron sufficiently strong enough to hold Las Vegas, would either hurt Syndrome or at the least keep him busy. Convince Rufus that as of the moment Sinatron is interested in cementing his base in Las Vegas, which is no different from what Doof is soing and building a sanctuary for capes, Sinatron could keep Syndrome busy, but that's only if he has a chance to gather resources and build up.
Fourth step Share the give the govement the means to produce Omnidroids with AI to sweeten the deal, gain more trust points with them. It accomplishes two things, one which is to give the remmants of America govermant more firepower, thus making Sinatron less dangerous , if he proves untrustworthy, it also weakens Syndrome by him no longer monopolizing omnidroids. In exchange Doof could have more leeway in other government involve masquerades such as access to aliens and other supernatural stuff.
Fifth step convince Shego about the enemy mine situation, such as Sinatron being another barrier against Syndrome if he manages to recover, Las Vegas being another safe zone for capes, Doof will share the spoils of what he found in Syndrome's gala with Shego, help Shego conquer Syndrome's power structure and help in science matters, in exchange for cape muscle, Shego will acknowledge that Doof is the overlord of the Tri-state area in theory ( while secretly Shego still has ownership of all her assets in tristate area) Something of a open house policy where Doof and Shego are allowed to operate mutually in the portion of the Tristate area- Shego owns) She can provide cape muscle when the time comes for a final attack on Judge Doom.
Sixth step, Doof and maybe the government and Shego will help Sinatron gain a foothold on Las Vegas, or sufficiently strong enough to exist as a faction. in exchange Sinatron will not mentioned anything about Doof's involvement with Syndrome, seriously that psychopath is willing to target families of his enemies, and kill capes just for existing. In fact it will be beneficial for Sinatron to have a consensual raid on Doof for starting resources (money stuff, robots, weapons) which Doof will allow occasionally , it will make it publicly clear that Doof is not involve with Syndrome's fiasco gala, Sinatron should also belittle Doof publicly to get others to underestimate him, plus it also gives Sinatron credibility which he will need.