He gets into his van and it blows up.

A short time after the hiatus, a new villain seems to appear. They pull their hood back to reveal… "It's me, Steven! It's me, Steven!! It was me all along!!"

With both of the explained possibilities below, and countless others I'm already thinking of myself, I honestly think Rebecca should have considered it a bit more before throwing away the opportunity.
For one, after announcing his tragic early death, and waiting a little while, they could have started a focus group of fans of Steven Universe, but instead of asking questions about the show, they would just have Rebecca walk in and say "I'm sure you're wondering why I've gathered you all here today. You see, Matt Burnett was not killed by food poisoning, he was, in fact, MURDERED!!! Lightning strikes exactly on cueAND THE PERPETRATOR IS IN THIS VERY ROOM!!! holyshit more lightning This would go on for quite a while before the reveal, everybody has a good laugh, instantly viral prank video.