Mark
Really wish we could all see these cats, I think majority of vets feel best option for severe C.H. cats is to PTS but they do not see first hand the wonderful quality of life they can enjoy.
C.H. affects the part of the brain which controls movement and co ordination due to cells not developing in that part of brain whilst in womb; cats are not blind because of this condition,in Minimopsicals case she had a seizure which caused temporary blindness, I find myself wondering why they are blind, I also cannot see what ongoing vet care they would need other than routine vaccs etc. Yes they do cost a little more for day to day upkeep due to toileting problems but little else.
Minimopsical cant walk properly its one step maybe 2 then fall over, she cant even squat to use litter tray, she lies on her side to piddle/poop, she can be very hard work but I know without doubt that she is happy and deserves her life.
You have a very tough decision to make and I feel your vet should enlighten you as to why he feels PTS is best, he should also tell you why ongoing treatment is needed and what for.
If I can help in any way I will, and God Bless you for agonising over this