Here are the basics. Archie and Veronica are struggling right now with their relationship and Archie doesn't want anything to shake things up too much. Reggie threatens to share some info that might make Veronica think less of Archie. In exchange for his silence, Archie agrees to drag race on Serpent Hill. Keep in mind that Archie is also racing for continued ownership of his 1969 Mach 1 Cobra Jet. (That's a car.)
Without getting too much into the details, the race began. A third car got in the way of the drag racers. An oil slick happened. And all three cars got crumpled.
Archie Comics wants you to know that Archie himself is safe. They're not killing off their star character again! Also, Veronica and Jughead are safe. They weren't at the race. Heck, Jughead was hardly in the book!
So it comes down to Betty and Reggie. I honestly don't see Archie Comics killing off Betty Cooper. After all, she's the co-star of at least two comic book digests and of a comic book that sometimes gets published! Meanwhile, Reggie is the bad boy that everyone includes in their list of core five characters and yet he's completely on the outskirts of life in Rivedale.
Plus, check out this image from the upcoming ARCHIES one-shot:
In other words, it's not looking too good for Reggie Mantle...
ARCHIE #20 is written by Mark Waid, with art by Pete Woods, and lettering by Jack Morelli.
Updated later on 05/19/17: I thought that the bass player in the above pic is Chuck Clayton, given the skin coloring. It's been pointed out by more than one person that I was stupid for looking at that pic and seeing Chuck. So there you go.