Note that uninstalling (or choosing to not install) any part of KDE PIM (KMail, Kontact, Korganiser, Akonadi, etc.) should not affect Plasma or any other of its components*. if it does, you should notify your distro, because that is a bug in the packaging.
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For example, the calendar that pops up when you click the digital clock in the panel, should not be broken. It just won’t show events or tasks from KDE PIM… Because PIM isn’t there. Otherwise it should be fine.