Emus do not die because they have splayed legs, people have their emus put down because they don't feel that the emu will have a good healthy life. Many people get their emus put down because they are concerned for the welfare of their emu and believe that it is cruel to keep an animal in a condition that won't allow it to indulge in it's natural instincts.
Emus are very active animals and love to run and play, if you feel that your emu is not able to live happily and enjoy it's self, maybe you should consider putting it out of it's misery. If the emu was in the wild it would not have been able to keep up with it's siblings as they grew stronger and faster and would naturally perish from predation. 
 
Unfortunately there is no way of curing splayed legs in an older chick as their bones have set solid and muscles have started to grow around the joints. If you were wanted to correct it's legs the vet would have to operate on the bird and pin it's legs back in place or break the legs and re-set them. This would take take a long time for the animal to recover from and would mean that it wouldn't be able to walk properly for a long time, and may never be properly cured of splayed legs. Which would be an extremely expensive course of operations and it may not be in the bird's interest. ( This is why many people often opt to simply having their chick put down if it has splayed legs, as it is less stressful for the bird and doesn't allow it to suffer unnecessarily).
 
Other people will probably disagree with me, but personally I would have the chick put down so it doesn't suffer any longer, because there is no point in keeping on to the chick in till it becomes incapable of doing day to day activities. In my opinion it would be unfair on the emu to keep it any longer, especially as you have noticed how it's condition is deteriorating. 
 
However if you think that the emu's condition isn't going to effect it's day to day life and that it is living happily, just let it live the end of it's days 
 
 
I hope this has helped, and I am sorry I couldn't offer you a positive answer to your emu's condition 
 
 
Clucksworth