Yes the Google Assistant is now missing from my library. When I add a "new" thing and choose Google Assistant it takes me to the screen that says "connect". Here it prompts me to "enable Stringify in your Google Assistant". Problem is I did this before I deleted it. Google can talk to Stringify but it looks like Stringify will not add the "thing" until I login again via the card in my Google Assistant (which won't show up now because I am logged in).
Here is a thought, what happens when you change the password on your Stringify account. Will Google require me to re-login?