It didn't seem to take a particularly large or well-equipped (on a galactic scale, anyway) rebel force to take them down in canon, so I'm sure another one would have sprouted from some out-of-the-way, uncaringly-opressed star system eventually. All it takes is getting lucky once or twice, and boom, no more Death Star, no more Emperor or Vader, radically different galactic landscape.
...That said, while the name of the team in charge would change, the Star Wars universe seems extremely resistant to actual meaningful political change, so whatever government came after the Empire probably wouldn't look that different in practice. It would honestly probably employ a lot of the same people, even, with unchanged views. I suppose it ultimately comes down to what you mean by the Empire "lasting".