Now, I realise this question is inherently unanswerable due to the classified nature of the mission, and speculation is also not desirable, but that's okay — because we can at least assemble official sources into something that resembles the most up to date information we have. So...
What was the outcome of the launch of ZUMA by SpaceX, to the best of the public's knowledge?
For those unaware, SpaceX conducted its 3rd secretive national security launch on January 4^th 2018, launching a payload known by the name of ZUMA, which was developed (including its payload adaptor) by Northrop Grumman.
Soon after launch, however, rumors started swirling that some kind of mishap had occurred. These were fanned hardest by Are Technica's Senior Space Editor, Eric Berger, who published an article entitled "It’s not official, but sources say the secretive Zuma satellite was lost", who suggested a number of possibilities, ranging from the payload failing to deploy, or some mishap with the Falcon 9 upper stage occurring.
Despite this, Elon Musk was more than happy to share mission success on social media, taking to Twitter & Instagram afterwards. Sources state that prior to the mission, he had also made comments about the importance of this specific payload to the company.
So, what do we know?
Again, please, no speculation. Hard knowledge and sources only — the more the better.