In the Avengers' eyes, Ultron had vanished completely, as if he had never appeared at all. But Tony Stark and the others no longer dared to casually continue the related experiments. One Ultron had already been this much trouble; if they created several more Ultrons, they would probably be even harder to deal with.
And most importantly, Tony Stark had no way to guarantee that everything Ultron had said before was true. Who could know whether there had been some other flaw in the experimental process, and that flaw was the real key to Ultron developing self-awareness and rebelling?
As a result, the Avengers began searching for Ultron's whereabouts on every front, while repairing Avengers Base and starting to build mechs again.
It could be said that although Ultron had yet to create an even greater crisis, his previous actions had already caused the Avengers heavy losses. Never mind that Avengers Base had almost been destroyed, causing who knew how much damage; the Mech Legion and the Flame Bio-Androids alone had taken the Avengers many years of accumulation to build.
The Mech Legion had at least shown traces of being deployed in supernatural incidents before, but the Flame Bio-Androids had been entirely one of the Avengers' trump cards. Moreover, compared with the Mech Legion, an army like the Flame Bio-Androids was what ordinary people truly regarded as a supernatural existence.
Although the Flame Bio-Androids were also creations of the technological side, the flesh-and-blood side's power of flame was indeed much harder to manufacture than the Mech Legion.
Just like that, time gradually passed. The Avengers were still hesitating over exactly what was going on with Ultron, and what kind of conspiracy he was brewing by disappearing so completely—until a mech appeared on the streets of New York...
Perhaps Ultron likewise