I don't think there ARE any definitive answers Mar---and I don't think it's up to the docs alone to say 'enough is enough'! Your husband should be the one to decide, in discussion with you, the rest of the family, and obviously his doctors. Do the benefits of further treatment outweigh the problems? Would he and you be happier having a 'peaceful/controlled' but shorter period together?
Before I even discuss the treatment options, I have told my family what I feel. Everyone is different and there are different ways of 'fighting'.
Statistics are only that--numbers that might apply to some, but not others, but the docs might be able to give you a 'rough idea' on his chances.
Read all you can and talk all you can would be my advice--for what it's worth--and I'm sure everyone eventually comes up--then questions--their OWN answers! There are some good, knowledgeable people on this site and some in your area who will talk to you 'better' than me, but just thought I'd reply NOW so you don't feel alone on this!
Brenda