A dental sinus lift may be in my future. what will happen if i do not have it done? also, will it result in post nasal drip, etc., ?

Sinus lift: It's hard to give you all the answers to your questions without the benefit of examining you and seeing x-rays. We can only guess as to your specific situation. Having said that, i see no relationship between needing a sinus lift & a post nasal drip. Sinus lifts are usually for the purpose of establishing sufficient bone for the placement of a dental implant. Not enough bone/no sinus lift/no tooth.

Why you need it.: Usually a sinus lift is actually opening the bottom of the sinus and adding bone to fill in part of the sinus. This is frequently done prior to placing implants if there is not enough sound bone available to hold the implant in place. There could be other reasons as well. If the area is sealed properly after surgery, then there should not be any communication from the sinus and your mouth.