The racehorse Paynter did fully recover from a severe case of colitis and laminitis that lasted two months. Even I was questioning whether the Zayats should've euthed him at one point. Now he's back in training and looking spectacular. So it is possible.
http://www.zayatstables.com/horses/paynter.html

That said I think the parading Oliver around on the Internets for donations was kind of tasteless.