The Wizard didn't destroy his life. We have to presume that no, he couldn't just come in a dream. He would have to judge each candidate in person to see if they would resist the temptation of the Orb of Sin. He obviously doesn't hand pick the candidate because he has a "spell of searching" or something that does the work of finding someone even open enough to except the magic, kind of like the Power Ring searching for the next bearer and not the Guardians. Plus he's ancient, he's probably long detached himself to how modern humans react to something like magic. As for timing, I assume after the seven symbols repeat seven times, the candidate is taken out of their temporal and spatial position, and after they are rejected, they are put right back were they left. After that, Thad spazzed out, Sid started being abusive, and Lionel didn't slow down or pull over. And even after they stopped, they were t-boned by someone else. I'm sure Thad never got to live that down. The Wizard probably couldn't have foreseen those chain reactions, or maybe because the need for a Champion against the Sins was just so great, the fate of one kid going mad isn't of his concern.
Actions have consequences, and The Wiz' is Sivana, so anything that happened was entirely as a result of The Wiz' actions
