Pay to blog plugin rules

Ok I will explain exactly what I need. I need blog admins to only be able to see the comment template on the main blog when they have paid to blog. when their pay to blog subscription runs out they should not be able to see the comment template any more.
in normal wordpress functions I think it would be
if (pay_to_blog(inactive) {
do this
} else {
do that
}
but I have no idea how your plugin determine when a blog is inactive and how to call that function.
Can someone please help me.