At first there's a true avalanche of questions you want answers to. What if you had, what if there was, if one could...
Unfortunately you haven't. There isn't. And you can't. One cannot rewind, cannot change the past. All we can do is learn from it, benefit from it, so that we can, with luck and pluck and self control, make the best of the future. There's but one "what if" question that may have some merit. What if you had died instead of your dog? You certainly would want your dog to recover from grief, would want him to smile, experience joy again. Is it so inconceivable that your dog does not want you to live life's next chapters not grieving, but happy, as fulfilled, as rich as the one you were allowed to share? It does not mean you have to forget. You never will.
I do not regard myself a religious person. I do believe that if there is something that controls life, our being, it is something so vast that it is beyond mankind's comprehension; it is not something that can be explained.
I don't know if the institutions of the many churches of christian faith know more than those of any other faith. If their representatives do truly represent, or if their aim, like that of their colleagues of any other denomination, is merely to direct society towards caring and benevolent behaviour.
After my dog's death I would have liked to ask someone in authority "Do dogs go to Heaven?" Then one day I typed the question into Google and found a lot of people - many of those famous for their wisdom and wit - have long pointed out, that this is entirely the wrong question, contrary to what the church would have us believe.
I don't know how other religions deal with the apparent difference between species. It appears though, that Christianity is, by far, the harshest religion when it comes to beings other than humans.

What you will find is that most [christian] practitioners argue animals have no soul and thus cannot be admitted to heaven. I've never heard anything more heartless, more un-christian. And more arrogant, or unqualified, for that matter. As there is no universally accepted definition of a "soul", as we don't know exactly what a soul is, I don't accept anyone can say those lacking one will not be admitted.
I know that the light in my dog's eyes, his joy, his love, cheekiness, the multitude of observed emotions, his character... all this is not the consequence of a few chemical compounds but a unique, a very complex soul. One that did not expire when his body did. Instead, it will always, and as much, be a part of me as all the others I love.