What are my chances, and what is the process like, to rejoin the Army if I'm 30% disabled?

Been in your shoes. Had the discussion with a couple guard recruiters. Depends on your Reentry and Separation codes. If your Reentry code is 4x, you'll likely need an Act of Congress. If your Reentry code is 1x, give your local recruiter a call when you're ready to head over to MEPS.

I can tell you from experience that my 4K KBK, the Air National Guard wouldn't even look at me when I was debating climbing back into uniform. I would have needed to go to a military records correction board to attempt to get my DD-214 RE code recategorized (possible, since I never went before a MEB before separating). If I got it upgraded, there was a chance I might have been able to reenter service. But, I wound up not pursuing that path, as other opportunities opened up shortly after that discussion, so I couldn't tell you how likely that outcome might be.

One thing I do know was said... Army's a little more lenient on what they can do to get you back into uniform. Regardless of anything I said, it's worth the time to stop in and talk with them.

It's not impossible. You'll likely just have more hurdles to jump than the average veteran.

Have you talked to a recruiter yet?