If they integrate Steamworks, these games usually (not always, but exceptions are rare) will not start up if Steam isn't running. I am speaking as someone who cares about and tests this.
Ironically, I have actually had far more success with stuff from the Epic Games Store. Lots of major titles such as Beyond Two Souls and Ratchet & Clank: Rift Apart function as completely standalone, DRM-Free binaries once downloaded, it's great.
The effect is the same if it means I can't launch my games without authenticating with a remote service that could go bust at any time, and has already dropped support for legacy operating systems which I still use.