In 2016 we moved khelpcenter from plasma to applications with the expectation that we'll simply let help requests fall back to the docs.kde.org website when khelpcenter is not installed (which ought to be the default expectation I guess since the unreliable state of khelpcenter is why it was dropped from plasma to begin with).

KInfocenter modules help however still 100% depends on khelpcenter

void KInfoCenter::helpClickedSlot()
{
    // Nicked from Ben, could not use KToolInvocation due to docpath.
    QString docPath = m_contain->helpPath();

    QUrl url(QStringLiteral("help:/") + docPath );
    QProcess::startDetached(QStringLiteral("khelpcenter"), QStringList() << url.url());
}