Upper jaw last wisdom tooth Gum line cavity. Dentist wants to pull, I want to save. Would tooth bonding be medically feasible?

Yes. it is possible to fill a wisdom tooth gum line cavity.  These are usually not visible so rather than bonding a high fluoride release restoration like Ketac Molar may be a better choice.Sometimes wisdom teeth need removal but decay is not a reason.  Root canal treatment and crowns can also be done on wisdom teeth.I have four wisdom teeth in my mouth and plan on keeping them for life.  They are harder to keep clean but it can easily be accomplished. 

Gumline cavities occur on all teeth in all areas of the mouth. Wisdom teeth are further back in the mouth and therefore make it more difficult to restore. The fact that it is difficult to restore should not be the only reason to extract instead of saving the tooth. If the cavity is a small one then I would attempt to restore it in order to try and save the tooth. If the cavity is significant and may involve a close proximity to the nerve or wrap around the tooth then an extraction may be more practical as well as beneficial in the long run.

A gum-line filling will be incredibly difficult to do properly on an upper wisdom tooth. You will most likely get a new cavity on that tooth soon after any filling is placed due to how difficult it is to keep that area clean. That's how you got the cavity in the first place, not being able to brush it properly. I would also suggest the tooth be removed. If the cavity gets larger, you could develop an infection. Infections in wisdom teeth can be very dangerous.