Suppose Job A has 2 downstream projects B and C. Project D should execute only after both B and C have completed. D should trigger even if either B or C or both fail.
A
/ \
B C
\ /
D

However with the current version of join plugin (1.15), D only executes if B and C are stable/success. If either of the downstream job fail, I get this message "Minimum result threshold not met for join project"

It will be good to have an option where user can force D to run even if B and/or C fail.
From he description of the Join plugin it seems like it should allow job D to run once B and C have completed (irrespective of whether they pass or fail).
"This plugin allows a job to be run after all the immediate downstream jobs have completed"

For example in the use-case where you want to fire an email notification after both B and C have completed OR send test results after B and C tests have been executed etc.

The code lies in https://svn.jenkins-ci.org/tags/join-1.6/src/main/java/join/JoinAction.java

Code:
Result threshold = this.evenIfDownstreamUnstable ? Result.UNSTABLE : Result.SUCCESS;
if(this.overallResult.isWorseThan(threshold))

{ listener.getLogger().println("Minimum result threshold not met for join project"); }

There should be an option to lower the threshold to Result.FAIL from the jenkins UI.