My hearts breaks for you. I had a similar situation with Quinn. What I expected to be a rather uneventful visit to the vet revealed he had a massive tumor. I had left him for evaluation, and got the news an hour later. My vet told me I could bring him home to spend a little more time with him over a Memorial Day weekend, but there was a chance his body would catastrophically fail, resulting in a painful death. I was not about to let that happen and elected to let him go as soon as I could notify my husband and get to the clinic.
I can understand your pain of not being able to say goodbye. We can’t know what our pets are thinking at such a time, but I firmly believe they have felt our love and take that with them as they transition. The shock and grief will eventually fade, but in the meantime, allow yourself to grieve. Please take care of yourself, though. I am concerned that you have not been eating. Remember that Ruby would want you to be happy and healthy.
You have my deepest sympathy.