American Idol has been going through some ups and downs ever since Season 8. The inclusion of the fourth judge in the first place had never been really needed. However, with the absence of Paula Abdul this season, Kara Diogourdi was the only judge needed to complete the triangle array of judges again.
This year, American Idol has remained with the idea of needing a fourth judge, and after going through a list of possible replacements for Paula, they came across Ellen. My only hope for her is that she'll at least make the show interesting and appealing while still giving a serious attitude on the contestants.
As for Simon, it was speculated since mid last year that he was going to be leaving American Idol after Season 9. It was said that his contract would be up while leaving it with him saying he was more occupied with a show he had going on in Europe, which proved to be true as we know it. As tough as Simon is, he can still bring out the facts and he can still make the show applauding. Though, without him, I can't say the TV series would remain as good as it is standing to be now, for the very least.
As for my opinion, without Simon and thoughts on going on to a Season 10 I say the show should stop here at the end of this season. It won't be the same, and I'm sure it will lose its fan base if it can't show to be as good as before. 2005 was American Idol's peak season, and ever since it started to plunder. Sadly, it hasn't gotten any better, and that is coming from one who enjoys the television show.
I think it would be smart to cancel the show after, or at least put it to an official end, and bring the "X Factor" over to the U.S. as a new show to bring out the unknown talent in people on FOX. At least, it would put something great to a satisfying end and introduce something new with possible popularity.