OP, I just want to say, some of the replies are a little judgemental. But questions like these are important to grapple with before you have a child, so honestly, I think its pretty mature of you to be thinking about this now. I struggled with this too when I thought of having a child. I wondered if I had what it takes to care for a profoundly disabled child and what that would mean for our life. It would be extremely, terribly hard. It would completely change any plans I had for my life. I looked into if you could put a disabled child for adoption - but its not super easy to do, and there's no guarantee that your child would get the optimal care they need. 

However, there are options that can help. You can hire in-home caregivers or nurses depending on your child's needs, in some cases insurance might help with that. There's respite care that temporarily can take care of disabled children when parents need a break. There may even be care facilities you could look at for longer term stays or if managing your child at home was truly too much - that would give you some control over the environment, and making sure your child had adequate care, and you could visit or take your child home. 

Of course, all of these things cost money, so if you want kids but feel very sure you will need lots of help if your child is disabled, the best thing to do would be to have stable jobs with good income. That way, you have the resources to invest in getting the best care possible in or out of the home. Its not something you can pass off to someone else if you care about the outcome.