Thank you for contacting us.
Changing this functionality will be considered a breaking change, as a lof of the Kendo UI users, are relaying to this functionality of the PanelBar control, so changing this default behavior will create a lot of inconvenience for other users.
I would suggest you to check our uservoice
section and post your suggestion there, so other people from the community can vote for it, and if it gets popular we will see it implemented in the future.
A workaround would be to manually walk through the PanelBar with jQuery and detect if you have not child items, then you can hide the node.
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