I made a quick tutorial I would like to share since this is something I didn't know till recently and I think its super useful and not well documented. Simply put, in zbrush you might loose your morph target or layer but were careful to keep your vertex order the same on a model. Here is how you restore it so you can work more non-destructively.
https://www.youtube.com/watch?v=Z_wCRAMEB8M
