Non interrupting task without end event, is it valid?


No, it is not valid. Add an end event following Notify user and it’s valid. The idea is that each branch created in the process must reach an end event, directly or indirectly. From the BPMN spec:


All the tokens that were generated within the Process MUST be
consumed by an End Event before the Process has been completed.


Thank you!

Just to be clear, by the way: since the boundary event is non-interrupting, reaching the new end event after Notify user will not end the process if the Make decision task is still open. It’s a “parallel branch” that runs to completion, but all branches must complete before the process as a whole ends.