Retiring or switching to the Army Reserves?

SGT David Sims you need to try and get that medical paperwork as well as all the other "proof" of service. Wether you decide to retire from the guard or transfer to the reserves ultimately by retirement you'll be in the Army Reserve in order to collect your monthly pension. Now if you're still in good enough shape to deploy and you still want to serve then transferring to the reserves might actually allow you to make SSG or SFC before you actually retire completely. Good luck as you make your way!

I'm not sure why you would need to get "medical paperwork" from your unit. In the case of almost any medical documentation, you would have originally provided a copy to them, you should already have that. If you do not have that, then you should be able to still go to the VA to start the disability determination, as any treatment provided by an MTF, VA or Tricare network provider would be documented and available to the VA in AHLTA.
As far as transfer vs retire, I assume you are in a state with no 92G positions above E5.
If you are currently BLC and SSD2 complete, you can also consider changing to another MOS, such as 92Y or 92A, 88M, or anything in your state that has potential for advancement, assuming you physically qualify for that MOS.
If this disability precludes you from deploying or changing MOS, then you should definitely consider retirement and disability.
Short of that, I am sure the Army Reserve has advancement potential in 92G somewhere, just depends on how close that is to where you live. You are a reservist, which means that your civilian career and the retirement from that is the most important factor, that is what pays your bills. Don't go chasing reserve opportunities across the country.