Hello - I felt I had to reply to this one as you are stressing out , I normally just read and them but move on.
I was in same situation in 2014 at around this time also having the same worries as you, I was in my 90 day period and struggling to find a job and sponsor. I was ringing immigration everyday trying to get an answer on the situation. Anyway I applied for my partner visa in the 90 day period eventually getting through to immigration with a bit of knowledge they put my worries to bed because I had applied for the partner visa and my 457 was current I still had 1 year left on it, the Government let you remain on the 457 visa.
You still need to find a sponsor to work but it takes away the 90 day count down. I still have the email immigration sent to me just incase anything pops up even though my visa was granted October 2015. Hope this puts your mind at rest a little.