It dont need to be you that delete it, i have noticed that Layer 0 disappears many times if there is Entety marker and Property Set in the drawing or in the Template, it dont need to have been used in the actual drawing.
It's only the layer that not show, so if i have some objects on layer 0, they are there, but i cant Select them or turn of the layer if i want before i make a New layer 0.
In metric system, dont know in English system, it was reported as a bug back then.
V18, V19, V20, V21, 2015/ 16/ 17/ 18 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB