I was flying around with my elytra and I noticed that it was low on durability. I had collected some phantom membrane to repair it when it showed the broken texture because I haven't seen it before. Then my elytra ripped I fell to the ground I had swapped it out for a chestplate and was holding it in my hand when it suddenly had disappeared I was confused on where the elytra had gone. Maybe I threw it by accident or put it in my ender chest but it was nowhere to be found

To reproduce: (from jirauser521040)

1. Create a world in creative
2. Equip yourself with an elytra and place a chestplate in your hotbar
3. Give yourself multiple stacks of rockets to fly
4. Change the gamemode to survival,  turn difficulty to peaceful, and turn on keep inventory
5. Activate the elytra and use the rockets to fly
6. Fly in a vertical direction as to give yourself more time to see the problem when falling. Reaching 3000 blocks high is a good point to be.
7. Continue flying until the elytra is depleted of durability
8. Once you have depleted the durability, the elytra will not turn into the broken elytra texture but rather will simply remain at zero durability. This however is a visual glitch and in reality there is no elytra anymore. This can be seen by attempting to swap the elytra with the chestplate in your inventory. 

Observed result:
When the elytra reaches zero durability, it simply gets deleted and no longer exists physically even if visually it is still present.

Expected result:
Once the elytra reaches zero durability, it becomes a broken elytra that can be unequipped and repaired at a later time. It should not be deleted or vanish in any case.