If they're not going to mass they're in mortal in. It is impossible for them to be "practicing" their faith and not attend mass.
I never said it was possible.
Now tell me how you know they weren't going to mass? The man sitting next to me goes everyday, but not at his Church. His Pastor would not know that. If he wanted to know, he could ask.
BTW, I have only been to Mass once this year. Am I in mortal sin? (I'm not RC, does that matter?)