Well, I just bought my 5D IV in March 2018, and I keep it positioned in the house for quick access, in case an interesting bird or animal makes an appearance outdoors. The lens normally affixed to my 5D IV? My EF 100-400L II IS, of course, which I have had since about August 2016. This combination remains second to none.
Some say the D850 is a better camera. Well, I bought a D850 in July 2018, and it is a truly wonderful DSLR, but my Nikkor 80-400G lens has a lesser Maximum Magnification, and a much longer Minimum Focusing Distance, so the 5D IV + EF 100-400L II IS is what I keep at the ready, when at home, and what I normally take with me on walk-abouts in nearby natural areas. (My D850 is usually paired with my Nikkor 28/1.4E.)
I hear/read the EF 24-70/2.8L II remains as relevant as ever. I tend to prioritize fast 35mm prime lenses, so have kept my older 24-105L, and recently added an EF 35/1.4L II.
Yes, Nikon recently announced a Z mirror-deprived system, and Canon then announced an EOS R mirror-deprived camera sytem, but either would be a step-downward/backward from your 5D IV. Welcome back, and, relax, as your gear is still good to go.
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I wore a police badge and pistol, and made evidentiary images at night, incorporating elements of portrait, macro, still life, landscape, architecture, and PJ. (Retired January 2018.) I enjoy using Canon and Nikon gear.