Part of the answer to question 1. is how much wood do you have left to work with. You need to remove a base molding or 2 to find out if there is sufficient wood remaining to even think about restoration. Most wood floors are supposed to be refinished every 25 years or so and this will result in the loss of about 1/8" of wood per refinishing. Asuming that you originally had 3/4" thick oak T&G floors, the wood was down to 5/8" thick in a refinishing about 1955. It might have been refinished again in 1980, or it might not have been. If it was, you could be down to close to the groove thickness if you refinish again. This means that a replacement is necessary. If it was not, you might be able to restore it now. You can "borrow" boards from one room or a closet to replace areas that are beyond refinishing.
Sorry, but I can't say much more than that without more info. You can get exact replacement material for complete removal and replacement of your floor, if you wish to go this way. The engineered wood floors that are so popular today should be considered as comparable in replaceability as carpeting.