@kuba
I am so sorry that you and your husband are going through this devastating medical condition. How quickly a person deteriorates depends on many factors and the best person to speak with would be your husband's Oncologist. Since you didn't mention Hospice, it sounds safe to assume that his doctor has not deemed your husband to die in the next 6 months, although of course, when we leave this earth, is not always up to the doctor. Hospice care does provide wonderful support when the time comes and I highly recommend that you obtain their services. Also, the dizziness and loss of balance needs to be addressed. Your husband could be dehydrated from the Chemo or other medications and these symptoms should be reported to the Oncologist who can provide treatment.
I know it's hard when you wonder " how many days do I have left" but here's a quote that I've always found to be very profound.
" Life is not measured by the number of breaths we take, but by the moments that take your breath away".
Sending a big hug to you today.