The screw fell out of my 2 yo implant while wearing temporary denture - Should I stop putting the adhesive over the implant area

I’m really sorry you’re going through this It could be very uncomfortable and unsettling to have altered sensation due to nerve damage. Although it doesn’t happen often, it is a risk that is important to understand. I personally don’t see it happening in our field often due to the car...

Existing teeth can be shaped to be utilized for tooth supported overdentures provided the teeth are in satisfactory health and are stable and have adequate anatomy.

The only option other than a dental implant would be a partial; however, partials are only intended for looks not function or bone loss prevention.

This is a little hard to diagnose just from a brief description without more information such as radiographs especially a CT scan. Best of luck with the treatment. Hopefully everything will go well with your case. 

Yes  you are going to have an overbite because it is your normal occlusion.  The doctor can improve it a bit with the final prosthesis, so that your smile is better and improve your aesthetics

Taking anti-coagulants will be a concern. I would suggest seeing a board certified oral and maxillofacial surgeon who does lots of implants. Many of them also have M.D. degrees. Have them do a complete exam and consultation and see what they think your options are.