I've only played the one year before, so I don't know if the "postseason" always works the same way, but last year, at least, it wasn't enormously different from regular season play. If you won your conference at the end of the regular season (i.e. after conference championships) or if you were in the top ten overall despite not winning your conference, you moved on to the regionals round, which if I remember right, was exactly like a regular season meet, except that only the top sixteen scorers (I think) from  "regionals" moved on to "nationals."  As with actual gymnastics, only your score for that day counted; your regular season score didn't figure at all. (This was one of many  lucky breaks for me, because some of my tougher competition got knocked out here.) Nationals was also more or less the same as a regular season meet, except that you counted four scores instead of five (because of how few people compete at nationals, relatively speaking). The score averaging cor0 mentioned was in full effect though, so if you had a gymnast compete in semifinals, Super Six, and event finals, as quite a few did, then your final score was an average of all three scores. 

Incidentally, I do think that everyone who didn't advance was allowed to "play along," submit a lineup as normal,  and see how things shook out, you just weren't in contention for the win.