Sunset provisions are used to ram mildly unpopular (or 'barely popular') legislation through congress. It allows opponents to save political capital for 'more important' issues, while at the same time getting to tell their constituents 'With my help, this mistake of a law will die in 10yrs (the favored sunset period)'. It allows proponents to pass such legislation with less of a fight, and say stuff like 'I helped get deadly assault weapons (sic) off our streets' (with a picture of someone firing a class-III full-auto uzi in the background) on TV, without actually doing anything...
So if the GOP holds either house of Congress, the AWB dies (and the gun industry will ramp up production of 'assault weapons' to prepare for the next ban). If the Dems get Congress, it all depends on GW.
And yes, the current AWB dies no matter what in 2004. To continue it, there must be a new law written and passed. And it's likely that the VPC and such will try to make the 94 AWB seem like a cake walk compared to what they come up with for 04...
The NFA was written in a 'different era' of politics, and passed without need of a sunset. The MG 'Making Ban' of 86 was tacked on to the FOPA (a law designed to remove some more onerous parts of the 68 gun control act), and has no sunset. That one needs to be lobbied away, if it is to go away. The only other way for it to die is for the 86 ban to be ruled unconstitutional (possible, but it will take a while, and some new federal judges).
Fortunately, WI's 'worst' gun laws are 'no loaded guns in cars', and 'no concealed carry'. There's no WI AW/Mag Ban, so if the AWB isn't replaced, I'll be off for a complete A2-style upper...