Can you explain to me why, if Sadducees did not believe in a resurrection, why would they follow the law? What motivation would they have if death ended it all. If there were no consequences for not following the law, and all meet the same fate - death, what motivated them?

I don’t know about the Sadducees, but by us in mainstream Judaism, we don’t do the mitzvot in order to receive a reward in the world-to-come, but rather we “do the truth because it’s true” (Rambam, Tshuva, 10, 2), out of true identification with the Godly ideals and morality of the mitzvot in this world, regardless of any reward or punishment. It may have been the same for the Sadducees, as well.