Hi, This is perfectly normal. Only the master is the contact point for the entire pool. I would advise to go for manual promotion if you consider your host dead. To do it, go on any slave you want to promote (just one) and type xe pool-emergency-transition-to-master. If you use HA, this will be done automatically, but HA can be tricky. The result will be the same, if the master is down, you'll lose the view in XO about what's going on the pool, until you get a master back.

@Cygace XO is not directly tied to XCP. So the versions have nothing to do with each other. You can look at the XO master commits and pick one that lists feat: release 5.xxx.x and that will line up with a XOA release. You can pick a version that is the same as the current XOA release and it will be the same tested base code.