You don't need to delete this manually. You pass this as parent in the constructor and Qt has this parent-child releationship where a parent brutally murders its children on desturction.

Why not keep it a QVector? We generally try to move away from QList

Looks like you're leaking the rules? Perhaps do a

qDeleteAll(m_ruleList)

in the destructor

I think doing

if (index < 0 || index >= m_ruleList.count()) {
    return;
}

is clear enough

Don't use this in conjunction with QML! This creates a nested event loop which will cause all sorts of hard to find crashes. You can probably just do the file selection on the QML side, like we do in most other settings modules:

import QtQuick.Dialogs 1.0 as QtDialogs

    Loader {
        id: fileDialogLoader
        active: false
        sourceComponent: QtDialogs.FileDialog {
            title: i18n("Import Rule")
            folder: shortcuts.home
            nameFilters: [ i18n("KWin Rules (*.kwinrule)") ]
            Component.onCompleted: open()
            onAccepted: {
                kcm.importRuleFromFile(fileUrls[0])
                fileDialogLoader.active = false
            }
            onRejected: fileDialogLoader.active = false
        }
    }

This is copied from another KCM and adjusted. It's behind a Loader as creation of this item is pretty heavy, so we want to just do it on demand. And on the import button you just do onClicked: fileDialogLoader.active = true. Perhaps you could share it for open and save, or just use two separate ones. I'm sure you'll figure it out :)