Hmm, interesting question. If Darla had been alive at the time, Angelus might well have sought her out. Even if it meant leaving Sunnydale and postponing his plans to harass Buffy. Though he would have regarded this vendetta as a program to purse once he had settled things with Darla. It's even possible that reuniting with Spike and Dru would have been that important to him (but of course Spike and Dru were already in Sunnydale and fighting against Buffy).
As for whether he would have tried to destroy the world--well, Angelus may be sire-whipped enough that it depends on whether Darla would want to do that. And she probably would like the idea--after all, she worked with the Master who wanted to make Earth into a hell dimension. So I say, yes.