Accidentally cancelled Xbox Live because I cancelled Ultimate

GamePass Ultimate includes both Live and GamePass. You likely would have been best to let it run until it ran out (turned off recurring billing) and then set up Live by itself again. But at this point you would need to set up a new Live only subscription.

I literally just did the same thing, so annoying because I had prepaid xbox live gold for a year. They should make it more clear before you cancel.

You can try contacting support to see if there is anything they can do, otherwise, you'll have to purchase a new subscription. http://support.xbox.com/contact-us

Update: I contacted xbox live support and they were able to sort out the issue. Quick and easily fixed.

Oh, that makes sense. But now that I have canceled the Xbox Game Pass Ultimate membership (and have been refunded the $1 it took to upgrade it), is the rest of my subscription gone?

If you cancelled ultimate yes, because when you paid the 1$ converted all in ultimate, by cancelling ultimate you are cancelling all subscription because ultimate is the 3 subscriptions in 1.