14 weeks post hair transplant and the donor area has depletion. Will it improve? (photo)

It depends on how many grafts were harvested.
You donor area seems to have been originally thick, so even if a lot of grafts (hopefully less than 4000) were extracted, it will still look ok! 
I would advice to be patient and wait at least 6 months, probably 1 year before you get disappointed. If it was a bit earlier, Minoxidil would help, at 14 weeks it might not be much help.

It is best to determine density of the pre and post op area.  It is difficult to tell, since I dont have a photo of or measurements prior to the harvest.

Thank you for your question.
The first thing I would do is go back to your physician and let them know what is happening.
I would want to do a pull test and get an idea what kind of shape the follicle is in. 
There is a strong possibility that you are experiencing Telogen Effluvium. If this turns out to be true, I would introduce laser treatments immediately to get the effected hair turned back to the growth phase.