As an 80-year-old Catholic, I was taught that missing Mass through your own fault is a mortal sin that, if unconfessed and unabsolved, could send you to hell forever. I know friends and other Catholics who are good people but no longer go to Mass. How could a merciful God condemn them to hell forever?
The obligation to attend Mass on Sundays and holy days of obligation is serious but must be understood in relation to other serious obligations. Caring for a terminally ill spouse or child is a greater obligation than attending Sunday Mass.