The 1994 AWB has nothing to do with the import ban. Two seperate laws. The 1994 AWB is found in 18 USC 922(v), while the import ban is 18 USC 925(d)(3). There is little left to agency discretion in the 1994 AWB, but the import ban is another story. The law empowers the Secretary (of the treasury) to only allow the importation of sporting firearms. The excat definition of a sporting firearm, however, is left to BATF to determine, thus they have great lattitude in determining what can be imported and what cannot.
Now,I am not 100% sure (because I've just been to busy and/or lazy to look it up), but I believe the "1989 import ban" as most people refer to it, is actually somewhat of a misnomer. I believe it was enacted as part of the Gun Control Act of 1968. It was by executive order that it was severly tightened up in 1989 when the president directed the Treasury to re-evaluate and adjust their definition of what constituted a "sporting firearm".
So even if the 1994AWB sunsets without revision or renewal, the import ban will still stand. In such a situation, a licensed importer could import weapons which would be "assault weapons" under the 1994 ban, but ONLY IF they weren't also precluded from importation by the 1989 ban. As it stands now, a licensed importer could do the same thing. There is no requirement that a preban under the 1994 AWB be in the US; if it was manufactured, legally owned, and met the definition of an "assault weapon" under the 1994 law, it is a preban, even if its been sitting in an HK warehouse in Germany for 10 years. The only thing preventing all those foriegn semiauto HK's, AK's, and AUGs from being imported is the import ban - the 1994 ban does nothing to keep those weapons out of the US. The 1994 ban only proscribes the manufacture, transfer, or possession of assault weapons, not their importation.