WS-Eventing section 3.1 specifies wse:Identifier: "In some cases, it is convenient for all EPRs issued by a single event source to address a single Web service and use a reference parameter to distinguish among the active subscriptions. For convenience in this common situation, this specification defines a global element, wse:Identifier of type xs:anyURI, that MAY be used as a distinguishing reference parameter if desired by the event source."

Three issues may be caused by removing <wse:SubscriptionManager> in <wse:SubscriptionEnd> per Issue (http://www.w3.org/Bugs/Public/show_bug.cgi?id=6397):
1)       It  may force a subscriber to create its own id and correlate it with the wse:Identifier returned by the event source. 
2)       It eliminates a common case where wse:Identifier alone can be used to correlate SubscriptionEnd and subscriptions;
3)       It creates backward compatibility issue when implementations use wse:Identifier in SubscribeEnd message;

Proposal:
Instead of removing <wse:SubscriptionManager> from SubscriptionEnd, move it to the WS-Addressing [source] EPR of SubscriptionEnd message.
This 1) preserves the wse:Identifier and 2) is consistent with the modeling of SubscriptionManager. The new message template looks like this:
<s:Envelope > 
  <s:Header >
    <wsa:From>
     <wse:SubscriptionManager>
        endpoint-reference
      </wse:SubscriptionManager>
    </wsa:From>?
    <wsa:Action>
      http://schemas.xmlsoap.org/ws/2004/08/eventing/SubscriptionEnd
    </wsa:Action> 
    
  </s:Header>
  <s:Body >
    <wse:SubscriptionEnd >
      <wse:Status>
        [
    http://schemas.xmlsoap.org/ws/2004/08/eventing/DeliveryFailure | 
    http://schemas.xmlsoap.org/ws/2004/08/eventing/SourceShuttingDown |
    http://schemas.xmlsoap.org/ws/2004/08/eventing/SourceCancelling
        ]
      </wse:Status>
      <wse:Reason xml:lang="language identifier" >xs:string</wse:Reason> ?
      
    </wse:SubscriptionEnd>
    
  </s:Body>
</s:Envelope>