"What happens if you don’t go to synagogue? Is that a sin? Does that mean you’re going to hell?” He’d been turned off from Catholicism after being told that skipping church on Sundays was a mortal sin."

 I'm not sure whatt "mortal sin" means in catholicism. In Judaism, there are only a few sins for which one must sacrifice one's life to avoid (e.g., idol worship, some sexual depravity? and something else that I can't recall right now). Not attending synagogue is not on that list