1750 ppm is what the salt should be. The range is between 1500ppm - 2000ppm. It will probably read low salt until you get at or close to the 1500ppm. You need to either get salt test strips, a Taylor salt test kit or bring your water in to a pool/hot tub store to have tested. Until then you're going blind.
I would expect a salt cell on a Sovereign to last in the 2.5-3 year range, but the output setting and how often/little you use boost will affect the life of the cell. If the cell is bad and you choose to not replace it, you will need to disconnect the power supply from the IQ2020 control box, remove the cell, get a new pass-thru plug and filter cap.