Verboten said:

... that the Empire is still around 30 years after Jedi, just seems stupid.

Enemies or peoples with different ideals don't automatically cease to exist after being dealt a blow in warfare.

North Korea is still a functioning country (and threat) 61 years after the end of the Korean War. Japan and Russia, among others, are also fully functioning nations and people 70 years after WWII. The Cold War also.

I think it's completely plausible that factions of the Empire would still be operating after Return. Mild threat, an uneasy peace, occasional terrorism, etc. That, to me, is another area where Zahn handled the sequels perfectly. The Empire isn't gone. It's just weak and angry.