Things go differently in the current canon, but what you described was more or less what happened in the old EU. There was no line of succession or instructions for what happened if Palpatine died. His death, along with Vader and important central figures in the Empire in ROTJ left a lot of squabbling Moffs and Admirals of dubious levels of competence in control of splinters of the Empire.

It wasn’t until Thrawn that someone competent started consolidating Imperial forces again.