As it always comes up and is confused, Denuvo is not a DRM solution but an anti-tamper product that encrypts the binary and provides developers hooks when tampering is detected.
It is often used in concert with DRM solutions - Steamworks, Origin, uPlay, etc - to protect those DRM implementations from being trivially cracked. Removing Denuvo wouldn't make a game any more or less "DRM-free" if the game had already been protected with a DRM solution.
This is what a lot of people initially thought but it's not true (or perhaps at least older iterations of Denuvo it was true?)
Upon launching the game for the first time the executable is patched by denuvo servers, you need an Internet connection for this, Steam doesn't do it, so if this doesn't happen, you can't play.
In fact, Steam now adds a strict Denuvo DRM label to games, if you look at Dishonored for example:
http://store.steampowered.com/app/403640/
"Incorporates 3rd-party DRM: Denuvo Antitamper. 5 different PC within a day machine activation limit".
If denuvo's authentication servers had to be down, you wouldn't be able to play it. From what I've read on the steam forums it's not a once-off check either, it'll check in the future again (granted it's not every time you play, so it's not that intrusive).