wildlife trip, you'll just have less pixel density (less megapixels) than a native DX-crop camera. Who cares though, the IQ per pixel will be superior.
As for the Z6 vs. DSLR?
You could probably search a decade of CB posts where I tout how an optical viewfinder is superior to digital. For many decades that was true, but today's mirrorless is a game changer. It's amazing to see your DOF, focus, and digital information in real time in the digital viewfinder of the Nikon "zed" series.
You want the Z6 over the Z7, not just for price (it's cheaper), but it's faster and if I recall correctly has an edge in 4k video. It's a better tool for wildlife. The Z7 is more a tripod/fine art camera.
Seriously, don't look at the Nikon DSLR series anymore. Your F-mount lenses will still work (yes, even the DX ones), but if you are going to upgrade....upgrade right.
Get the Z6 Mark 2.