NIK where are you?

[hannisian]

I just updated PS, and cannot find my NIK plug-ins.

[Test Screen Name]

Reinstall your plug-ins each time you upgrade Photoshop. Keep the installers! But don't expect Nik to fully work.

[hannisian]

I did that before I asked my question. Perhaps PS 2018 just does not support NIK. If so, how do I go back to the prior version?

[Eggy21]

I have the latest CC 2018 and the NIK filters are working fine (win10).

[Test Screen Name]

Many people are running Nik successfully with PS 2018 (except the bits that cause a crash). 

You can go back to the previous version of Photoshop (or keep both) using the Creative Cloud app. It has options to download old versions, and to keep old versions on upgrading.