What if I really don't have it in me to cope with this?
Then you abandon your kids. You leave them with a Mom that they have to take care of insted of someone to care for them.
I hear your pain, esp about your Dad and then to have this happen with your H. Perhaps your lesson in all of this pain and agony is to find your own strength. Life has a way of throwing things at us until we "get it". The lessons will come at you in many different forms until you do or until you die.
Do you meditate at all? I've found this is a really helpful way to be introspective and to figure out things about myself and my life.
What would you like with regards to visitation? Heck, stack the deck in your favor and then negotiate it. See just how accomodating he's really willing to be.
You are stronger than you know. You choose the strength. If your H had died, what would you do? You would grieve and then carry on, for yourself and for your kids.
Just an aside, have you seen the movie "Crazy, sexy cancer"? Life is all about perspective.