(((((Hugs))))) and prayers to you, your son's father, and your precious son. More for Grandpa, who is likely hurting as badly as you are.
It's hard to say what his outcome will be, sometimes very young children make miraculous recoveries and sometimes they are left with davastating disability. The thing is, no matter how it turns out, he is still your little boy and you will find joy with him in life.
I am a special education teacher and have worked with many different types of disabling conditions; some very severe and others mild. I want to tell you that there is worth and love in every single life. From the middle school aged boy, who was oxygen deprived during an operation, who couldn't talk, but could sit with the band and use his foot to play the bass drum in perfect time, all the while smiling hugely- to the little girl I was told was too retarded to talk, but did, after her and I sat day-after-day in a quiet hall alone, while I held up common things and over-enunciated the words over and over. Or to the boy who the doctors said was going to die from some very rare disease within 2 years, that was 17 years ago, when I saw him in the store a while ago back he took my hand and hugged it, whispering my name. Their families learned to live with what life dealt them, and the children develop special bonds with those who love and care for them.
Contact the agencies that can assist you and him, such as the regional center, the social worker at the children's hospital can help you.
Life isn't the same for everyone. His will be what the Heavenly Father ordains. You will both have lessons for each other and trials to weather as he recovers. Never give up! That's not denial it's hope! Have abundant hope and love for him.
Please please forgive his grandfather (and the cats!).
I will continue to pray for your little guy and hope for one God's special miracles!