I just talked to Dad. He had just woken up and was pretty out of it.
Mom emailed last night to say he didn't eat at all yesterday, and he slept more than ever before. He was fidgety, wanting to get out of bed, and even succeeded in pulling off his hospital gown (the nurses compromised with a sheet across his middle). All these things are consistent with the end.
In other words, he has taken Teagan's advice and packed his snacks and stuffed animal for the journey to heaven. He's got his umbrella, and he's ready for his next adventure. My guess is that his train will leave any moment now.
Bon voyage, Dad. I love you.