I am wondering if she is still a bit groggy from sleep and misinterpreting what is happening. I know Basenjis do seem to sleep through things when they are warm and comfortable, and I might be inclined to give her the benefit of the doubt until I was sure what was going on. Does she get over the aggression quickly when you say "no", or does it continue? Perhaps she is afraid he is going to remove her from her warm comfy bed? If so, she indeed thinks she has "won" when he leaves!
You could try getting up yourself to say goodbye to him, and see what her reaction is to that. But the leash is a good idea and will give you a way of removing her without risking a nip. If you do remove her from the bed, don't let her get back in without "earning it" in some way. (can be as simple as obeying a command to sit, but she needs to do something and you need to make it plain it is the "price of admission" and that it is you who is in control, not her.)
What is your usual routine in the morning when he isn't leaving early? Does Macy get up before or after you do? You mentioned that you know not to disturb her when she is sleeping. Including in bed? Does she react if you try to move her over when she is sleeping? (I just shove mine out of the way when his leaning on me becomes uncomfortable, and he does not resent this…...but he does try to sneak back).