I am sorry about Bear. He has done so well over the years, and you have helped him live a good and full life.
It is never easy when we have to face them leaving us soon.
I don't suppose there is any possibility of postponing your vacation?
Bear obviously means so very much to you, and there is a chance he may not last another month. Of course, I hope he does, and with decent quality of life or as long as possible. But there is that chance. How would you feel if you left, and came back and he had passed?
Sometimes that can happen with a dog who isn't doing too badly, but is nearing the end of life. They pass when their family is away.
That can cause so much recrimination after they have gone, and make grieving harder.
It may also be important at this stage to keep a close eye on him day by day, as an illness can suddenly take a turn for the worse, and a clear decision might have to be made then.
I do feel all that would be easier and more "organic" if you were with him, rather than being forced into such a decison from a great distance over the phone for example.
And he needs you. His last days....weeks (hopefully) are very precious and it might bring you some comfort after he has gone, that you watched over him as his life drew to a close.
Re: his quality of life.
Obviously he still has a decent quality of life, and is able to enjoy some things. There are those who would disagree with me, but where there is life, there is a right to live.
As I said, that could turn "on a dime" at any time.
One thing that will seriously lower his quality of life will be if nausea takes over. Now to some extent ant-nausea drugs can help, but if it gets to the stage that they don't....then there really are few options for extending his life with quality of life.
That's why he will need to be carefuly observed by someone whom he loves, and who loves him.
If you do postpone your vacation, don't think of it as putting a "dog" before your life, but as standing by a dear friend in his last days.