Hey guys, you can render out seperate depth file. To do this you must render out in a file format other than RLA and IFF which have the Depth in the file. If you use something like a tif it will render out a seperate file.

e.g.
untitled.tif
untitleddepth.iff

It should create a iff file for the depth

After effects does not seem to handle iff and RLA depth files well so you must extract seperate.