IMHO, Riley was simply waiting until he had finally assembled a team capable of winning before resuming the coaching job, which his ego demands. It will also improve his winning percentage, waiting to take over when the team is ready, much like Phil Jackson.
He has proven himself to be a great coach with the showtime Lakers, Much, much better than that phoney Phil Jackson.
I doubt that Riley will try to impose that great a discipline on Shaq. I'm pretty sure that Riley spoke with Shaq and Wade and tested the waters with them before making this move. You don't wear down a 300 plus pound center in practice when he gets to be a certain age.
It would not surprise me one bit to see the Heat make it to the finals. I already picked them in the beggining of the year.
Riley will find the way to get the most out of the new additions, Antoine Walker, Gary Payton and the others.