The thing is.....We, the viewing public, saw someone inject Steve's IV with a drug.....it slows your heartrate down so you appear dead (Yes, I read this as details in a few books, too). So, the fact his coffin was switched was no surprise, most folks knew he was still alive, just did not know "who" did it, who had him. So it was always known he was still alive, which of course had all the Steve/Kayla fans waiting with hopeful hearts for his return.
As to Will, I thought Will went to California with Sami AFTER he & Sonny were married. He had already written his piece on Paul, thus was asked to write the script for the movie on Sami's life or whatever. In CA, he was distant, would not call Sonny, or answer his calls, or texts, or rarely did. After he got fired, & came home dejected, then we learn he cheated on Sonny in CA.