Please give a medical explanation of how a hematoma heals, how long it realistically takes & possible effects on final results?

It seems that you're unhappy with your recovery. To answer your one question, usually hematomas are not common. It is a  known complication that can occur after a neck lift or face lift procedure however. They are more common in people who have uncontrolled high blood pressure as well as male patients.
Small hematomas usually resolve on their own. A large hematoma or an expanding one must be surgically evacuated. Hematomas do cause a delay in the healing process but a lot of times those patients end up with extra scar tissue underneath and actually end up with a firmer appearance where the hematoma was.
With newer techniques in my practice, usually I do not use any drains after any facelift or necklift surgery.
If it does not settle, you can undergo correction with aspiration or with additional surgery.  I would recommend that you see a board-certified plastic surgeon in your area that is a member of both ASPS & ASAPS and performs a lot of facelifts if you want a second opinion and of course, make sure you follow up with your own surgeon and talk about this. 
I hope this helps and wish you all the best in your surgery and event. If it does, please take a moment to up vote this answer on the “respond” button on the top right.  

At 3-4 months after surgery small hematomas and edema has mostly resolved.  If you still have irregularities it may be due to scarring or scar tissue related to the fluid collections.  You may require a small revision to recontour your neck. 

A  Hematoma is a known complication that can occur after a facelift procedure, and is more likely to occur on a male facelift, than a female facelift. In our practice we use  Jackson Pratt drains to help prevent it, but they can still occur in the first 24 to 48 hours after the procedure. Small hematomas are addressed by placing pressure on them and they resolve on their own. A large hematoma must be surgically evacuated to remove the  blood clots from underneath the skin. Although there may be a  slight delay in the healing process with lumps and bumps underneath the skin first few months,  most patients resolve quite well