Thanks, guys. If I'm unable to get XAPI up and running I may look at involving HA-Lizard support. I'm taking things cautiously at the moment as my VMs are still operational, so I've got a bit of time to find the best approach.

I should mention that I'm able to access the host via Putty, I just can't connect via XenCenter. I tried restarting XAPI, the toolstack, and the host itself.

Here is the result of service xapi status:

● xapi.service - SYSV: XenServer server
   Loaded: loaded (/etc/rc.d/init.d/xapi)
  Drop-In: /etc/systemd/system/xapi.service.d
           └─local.conf, slice.conf
   Active: failed (Result: exit-code) since Tue 2016-12-06 13:53:37 GMT; 3h 0min                                                                                                                                                              ago
     Docs: man:systemd-sysv-generator(8)
  Process: 16999 ExecStop=/etc/rc.d/init.d/xapi stop (code=exited, status=0/SUCC                                                                                                                                                             ESS)
  Process: 16990 ExecStart=/etc/rc.d/init.d/xapi start (code=exited, status=0/SU                                                                                                                                                             CCESS)
 Main PID: 16997 (code=exited, status=2)