I'm not sure I completely understand the OP's circumstances, but is it correct to assume that, because you and DH have some disabilities, you both have/had concerns that your child will, as well? That's a valid concern--even perfectly "normal" people can have a child with disabilities. If these concerns led to the vasectomy, and your DH is happy with that, then I don't think reversal is a good idea. For one, your DH doesn't want kids. Secondly, the disability thing could be valid (depending on the specific nature of the disabilities, and I don't want to pry into your personal circumstances). Not only would a child with disabilities be more work, even the easiest child on the planet is a LOT of work, even for young, healthy, active parents who don't have any other challenges.
The other thing is, if the nature of your disability is such that parenting would be a challenge, I don't know if fostering or adopting is going to be a viable choice. First off, your DH may not want these things, either, since he didn't want biological children. Beyond that, it may be extremely difficult for the two of you to jump through the necessary hoops to qualify for adoption--and adoption can come with its own challenges. I'm sorry if this upsets you, but I'm trying to be honest and realistic.
I also don't thin kit's fair to try to talk another person into making a choice that they clearly don't want, such as your DH in this case. You agreed to the procedure years back. He's happy with the status quo.
There may be other ways to fulfill the desire you have. Volunteering with children or adopting a cat or dog might go a long way for you--added bonus, they require a lot less care. Good luck to you.
I see your point. 
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