I feel very strongly that you have to stay with your husband. Your daughter has her own husband and a joyous occasion to celebrate, she will hvae so many things to do, people to see, etc. Does she understand how ill your husband really is? (is your husband her father?)
I would never have dreamed of leaving my husband when he was ill. When he became ill before diagnosis, - he couldn't eat and felt sick - I was extremely busy at work and I really didn't give him enough attention. When I began to realise that this was serious and became worried, my husband told me (sobbing) that he had never 'felt so lonely in his life' as he had felt during that week. Serious illness isolates the sufferers and they need somone to be there for them.
Your husband has a very serious illness and he knows the outlook is poor. I am sure he feels afraid depressed and isolated - even from those he loves. You are his pillar of strength, his support and consolation, - bluntly he needs you more than your daughter.
Also, his state of mind is an important factor in his ability to deal with his illness. If he is left alone he may easily become depressed and angry. I think unequivocally you should stay.
On a practical point, why not set up up video cam and link with each other through your computers. One of my neighbours talks to his son in Canada (from the UK)weekly over the internet. With video cams he is able to see his new grandchild growing and the contact feels more 'real'.