Eh. Maybe lost, maybe a cover story to try and hide a school-bus sized satellite in LEO (or thereabouts).
The back-room part of this story is the one I hope to hear some day...
1. "Hey Elon. We are gonna say the satellite never made orbit."
2. "Don't tell Elon, but we are gonna blame his rocket for failing to deliver Zuma into orbit."
3. A poorly-designed latch failed to allow the satellite to separate from the rocket, and both burned up on re-entry.
In Option 1, there has to be a pretty big secret deal on the back-end, if Elon is going to allow them to say their rocket failed after a long series of successes. And his entire future business of SpaceX being built upon the image of reliability and success.
In Option 2, you gotta be pretty goddamn stupid to sabotage your ONLY heavy-launch provider's business and reputation.
In Option 3, SpaceX has an incredible history of public disclosure of every single failure it has had, and how it has learned from each failure. This could get really sticky, because at some point it is going to come down to either SpaceX making a mistake in their latch design, or the DOD making the mistake. Neither is a better option. (Remember when the Mars lander plummeted into the surface like a bullet because one organization was using Metric, and the other was using Stupid American Units? Yeah. That's gonna be remembered for EVER.)
And finally, I don't know the math (KB?) but a spy satellite of that size, with that much power and payload inside of it...? I'm not sure all/most of it would burn up on re-entry, because I don't think it got high enough, or fast enough, to get the heat up in the "destroys everything" range.
That leaves debris on the ground/in the water. Sensitive military debris.
Can you say Glomar Explorer? Or Kursk?