I'm sorry. I know how hard it is to lose one after fighting to save it.

I would strongly suggest getting a necropsy done, especially if you have other snakes or even if you plan to get other snakes, as many viral diseases present as RI's but they would not respond to antibiotic treatment.

In going through your posts since August I strongly suspect either this snake was sick when you bought it, or the stress of being rehomed was enough to depress its immune system so the illness could take hold.