No way. KHTML is a cautionary tale of what happens when open source is coopted by corporate power. How can you call KHTML successful when it is dead, with its progeny in tight control of Google/Apple?

Because it formed the basis for essentially every web engine that is used today? I would call that successful.

(Before you say "but gecko!", take a look at the usage stats.)

Success is subjective. But I don't think it was an intention of KHTML developers to build a basis for corporate-controlled browsers and then die.