Fixed upstream:

https://github.com/virt-who/virt-who/commit/88f8f4e2f4dd92615d7922e4282da038491a5727

The previous commit doesn't handle it very well, this one should be better:

https://github.com/virt-who/virt-who/commit/eb66da3d8f89307835dcb1cfbd5a715e4487d19e

Fixed by rebase to virt-who-0.16-1.el6.

Reopen it on virt-who-0.16-4.el6.noarch since virt-who cannot detect the hypervisor has been deleted also cannot send any error info in the log.

Rechecked version:
subscription-manager-1.16.8-2.el6.x86_64
python-rhsm-1.16.6-1.el6.x86_64
virt-who-0.16-3.el6.noarch

Rechecked process:
1 Register system to stage candlepin.
2 Configure virt-who monitor hyperv.
[root@sgi-xe500-01 run]# cat /etc/sysconfig/virt-who  | grep -v ^# | grep -v ^$
VIRTWHO_DEBUG=1
VIRTWHO_INTERVAL=2
VIRTWHO_HYPERV=1
VIRTWHO_HYPERV_OWNER=7715246
VIRTWHO_HYPERV_ENV=7715246
VIRTWHO_HYPERV_SERVER=10.73.5.212
VIRTWHO_HYPERV_USERNAME=administrator
VIRTWHO_HYPERV_PASSWORD=Welcome1
3 Restart virt-who 
[root@sgi-xe500-01 run]# service virt-who restart
4 Delete the system using the stage candlepin site
5 Check the virt-who log in rhsm.log
[root@sgi-xe500-01 run]# tail -f /var/log/rhsm/rhsm.log

Result:
virt-who cannot send log message stating that communication with rhsm failed because the consumer no longer exists. it repeat send normally info in the virt-who log as the following:
2016-02-25 20:56:25,935 [virtwho.env_cmdline DEBUG] HyperV-1(3085):MainThread @hyperv.py:retry_ntlm_negotitate:67 - Using NTLM authentication
2016-02-25 20:56:26,509 [virtwho.env_cmdline DEBUG] HyperV-1(3085):MainThread @hyperv.py:retry_ntlm_authenticate:80 - Sending NTLM authentication data
2016-02-25 20:56:26,810 [virtwho.env_cmdline DEBUG] HyperV-1(3085):MainThread @hyperv.py:retry_ntlm_authenticate:103 - NTLM authentication successful
2016-02-25 20:56:32,623 [virtwho.env_cmdline DEBUG] HyperV-1(3085):MainThread @virt.py:enqueue:351 - Report gathered, putting to queue for sending
2016-02-25 20:56:32,625 [virtwho.main INFO] MainProcess(3077):MainThread @virtwho.py:run:305 - Report for config "env/cmdline" haven't changed, not sending

You have to do some change in host/guest association (start some VM), otherwise the report is not sent ("Report for config "env/cmdline" haven't changed, not sending") and this bug won't trigger.

Checked it on virt-who-0.16-7.el6.noarch,when mapping info update, virt-who can show error info after delete system on satellite web UI, error info as the following:
2016-03-16 01:40:46,376 [virtwho.main ERROR] MainProcess(26864):MainThread @virtwho.py:send:203 - Unable to send data: Communication with subscription manager failed with code 500: undefined method `inject' for nil:NilClass

However, the error info is not clear, would you mind to stating that "communication with rhsm failed because the consumer no longer exists."

This looks like you're facing some bug in candlepin. This error is returned by candlepin: "undefined method `inject' for nil:NilClass". What candlepin version do you use?

Verified it on virt-who-0.16-7.el6.noarch against latest stage candlepin since it will state "Unable to send data: Communication with subscription manager failed: consumer no longer exists" if system has been delete from web UI when host/guest updating on hyperv/esx. Therefore, verify it.

Verified version:
virt-who-0.16-7.el6.noarch 
subscription-manager-1.16.8-7.el6.x86_64 
python-rhsm-1.16.6-1.el6.x86_64

Verified process:
1 Register system to stage candlepin.
2 Configure virt-who monitor hyperv.
[root@sgi-xe500-01 run]# cat /etc/sysconfig/virt-who  | grep -v ^# | grep -v ^$
VIRTWHO_DEBUG=1
VIRTWHO_INTERVAL=2
VIRTWHO_HYPERV=1
VIRTWHO_HYPERV_OWNER=7715246
VIRTWHO_HYPERV_ENV=7715246
VIRTWHO_HYPERV_SERVER=10.73.5.212
VIRTWHO_HYPERV_USERNAME=administrator
VIRTWHO_HYPERV_PASSWORD=Welcome1
3 Restart virt-who 
[root@sgi-xe500-01 run]# service virt-who restart
4 Delete the system using the stage candlepin site
5.In hyperv, start/stop/pause guests.
6 Check the virt-who log in rhsm.log
[root@sgi-xe500-01 run]# tail -f /var/log/rhsm/rhsm.log
2016-03-30 02:30:35,101 [virtwho.main INFO] MainProcess(12420):MainThread @subscriptionmanager.py:hypervisorCheckIn:185 - Sending update in hosts-to-guests mapping for config "env/cmdline": 1 hypervisors and 2 guests found
2016-03-30 02:30:35,101 [virtwho.main DEBUG] MainProcess(12420):MainThread @subscriptionmanager.py:hypervisorCheckIn:186 - Host-to-guest mapping: {
    "564D80F1-61F0-8510-87BF-57F9EC6122D7": [
        {
            "guestId": "C877953C-A19E-5149-B614-D97873C4CBD2", 
            "state": 1, 
            "attributes": {
                "active": 1, 
                "hypervisorVersion": "6.3.9600.16404", 
                "virtWhoType": "hyperv", 
                "hypervisorType": "hyperv"
            }
        }, 
        {
            "guestId": "8329390B-8359-F646-9176-27D738580E81", 
            "state": 5, 
            "attributes": {
                "active": 0, 
                "hypervisorVersion": "6.3.9600.16404", 
                "virtWhoType": "hyperv", 
                "hypervisorType": "hyperv"
            }
        }
    ]
}
2016-03-30 02:30:35,862 [virtwho.main ERROR] MainProcess(12420):MainThread @virtwho.py:send:203 - Unable to send data: Communication with subscription manager failed: consumer no longer exists
2016-03-30 02:30:35,863 [virtwho.main DEBUG] MainProcess(12420):MainThread @virtwho.py:send_report:168 - Report from "env/cmdline" failed to sent

Result:
No stack trace. There is a log message stating that "Communication with subscription manager failed: consumer no longer exists"

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHEA-2016-0859.html