The child node of parsys with specified name 'par' is not created until you add a component inside the parsys. That's the default behavior of parsys. In this case, its throwing error because of missing child component and unable to locate the path of parsys which you have seen in console logs. Once you have added child component, the parent container allows the parsys to be deleted without any issue. This could probably be a bug. You may log a ticket for same.
If you add unbalanced div tag, that would break DOM structure and create other issues.
Temporary workaround - Drop a component inside parsys and then delete it, per your use case, till the time you get a fix from customer care.
I tried your workaround by adding some component in parsys (hence the node "par" will be created). Once I delete the whole component it disappears from the page. However, on refresh of the page, the component is again visible. (the component is not deleted from CRX)
Added an image component in child parsys.
When I delete the component, it disappears from the page.
If I refresh the page again, the component is visible.
However, the child "image" component has been deleted.
I would recommend to log a ticket wit daycare and ask for the patch.
You could obviously overlay '/libs/cq/gui/components/authoring/editors/clientlibs/core.js' & fix it, if that's critical. This doesn't seem to be a showstopper for authors to continue. The developers could delete it from /crx/de as and when required.