Filing this after talking to Meni Hillel and Steve Watanabe this morning based on the comment here at: 
https://issues.couchbase.com/browse/MB-37842?focusedCommentId=494107&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-494107

Steps to reproduce
1. 3 node cluster .215 .217 .219
2. Split brain .217 by blocking traffic from .219 on .215 and vice-versa
So now we have two cluster halves:
First half - .215 and .217 with .219 unresponsive
Second half - .217 and .219 with .215 unresponsive
Now it appears that we can't (unsafe) failover .215 (orchestrator) node out of the cluster as these options will fail

Option 1: Unsafe failover request to .215/.217

curl -v -X POST -u Administrator:password http://172.23.105.217:8091/controller/failOver -d 'otpNode=ns_1@172.23.105.215' -d 'allowUnsafe=true'

will fail as:

Unexpected server error: {error,

                             {not_in_peers,'ns_1@172.23.105.215',

                                 ['ns_1@172.23.105.217',

as .217 and .215 think that orchestrator (.215) is healthy

Option 2: Unsafe failover request to .219

curl -v -X POST -u Administrator:password http://172.23.105.219:8091/controller/failOver -d 'otpNode=ns_1@172.23.105.215' -d 'allowUnsafe=true'

won't return a response as ultimately the request tries to get routed to .215 and it cannot communicate with it.

Option 3: Do a regular hard-failover of .215 by making a request to .217 node

curl -v -X POST -u Administrator:password http://172.23.105.217:8091/controller/failOver -d 'otpNode=ns_1@172.23.105.215' 

will fail as:

Failover exited with reason {{badmatch,

{error,

{no_quorum,

[{required_quorum,

[majority,

{majority,

{set,2,16,16,8,80,48,

{[],[],[],[],[],[],[],[],[],[],[],[],[],

[],[],[]},

{{[],[],[],[],[],[],[],

['ns_1@172.23.105.217'],

[],

['ns_1@172.23.105.219'],

[],[],[],[],[],[]}}}}]},

{leases,

['ns_1@172.23.105.215',

'ns_1@172.23.105.217']}]}}},

[{failover,deactivate_nodes,2,

(Note that we can unsafe failover .219; that works fine. The issue here is that we can't get .215 (orch) out of the cluster)

Logs attached