JLU might be dead, but just like comic books, dead isn't always dead. Mattel could always trot out some future SDCC or con exclusive JLU stuff if they wanted to. They have all of those expensive molds after all.
Regarding a JLU sub, Mattel could easily have set these last six three packs up as a mini-subscription. I would certainly have preferred that: One order for six packs instead of having to come back to the Matty site once a month for the next six months. It's not as if they're getting any more of my money after JLU's final run. If it ain't JLU, it ain't on my radar.
If it were at all possible, I would even say that Mattel was entertaining the sub possibility for these. The only real hindrance to that would be the lack of a sub exclusive item, such as a Volcana. Now that would have been cool.
_________________ '...because the minute a little girl is trampled by 100 teenage girls trying to get to Justin Beiber at the Tea Cups, you will be wondering why the hell we make poor Justin Beiber stand in a 30 minute line and create an unsafe atmosphere.'