Gambler boy won't die in 1 chapter, I think. But if he dies, he dies. As with all comedy manga, it's important to pace the swapping - lest the formula gets stale fast.
Note that J learned a bit more... humanity while being a little girl (the .5 chapter with shoujo novels was hilarious). It is actually gonna suck for him to go back to being a middle aged dude again after running around in the body of youth and a woman in her prime (albeit he'll probably appreciate the strength and his m1911s better). Megumi actually hasn't seen much of adult life even in J's body - she literally became a NEET (albeit an intelligent one). Strangely enough Megumi probably has the least development and growth thus far - while J is seeing other potential to life beyond die hard and hard-boiled. Marie herself however, may have learned firsthand how insane tiger moms and reckless men can be. Marie likely won't ever have kids herself - unless she decides to quit the assassin life.
A part of me wonders if Marie and Megumi are related in some way - given the white American dad and Japanese mom... and raising them harshly as separate single parent. How ironic if they turned out to be distant sisters or cousins?
Off-topic, but related, if anyone is interested in "hard-boiled" Asian/Hong-kong Crime-Noir action movies, Chow Yun-fat with Director John Woo was probably the best combo from the 1980s. (A Better Tomorrow 1/2).