I’ve never understood this idea that mortal sin is a complete rejection of God – or that you would have any interest in taking communion if you HAD completely rejected God.
I don’t always do what my parents tell me to do. This is not a complete rejection of my relationship with them. It’s just a natural consequence of free will.
Similarly, while I have committed mortal sins, I’ve never felt any particular absence of God in my life as a result afterward. Guilt, sure. But not a loss of faith.
While I suppose you could just be a crazy person who hates God and takes communion anyway to stick your thumb in his eye, it seems like the very thought of wanting to take communion would indicate you haven’t completely separated yourself from God. And if you still value your relationship with God enough to want it, why would it be bad to take it?