No. No, no, no, with a side of no sauce and a serving of no.
There are few things more emotionally confusing than boning your ex, even in the most flagrant "God I Just Need Some" circumstances, even if you both establish very clearly that you're not interested in getting back together, because at least one of you is lying on some level.
Keep in mind, this was a relationship that ended for a reason. Maybe you grew apart as people. Maybe you got bored with each other. Maybe he was forced to return to his home planet. Regardless, the point is, the relationship didn't work, and doing your ex just stirs up a lot of emotional mud that should have settled in your mental lake a long time ago, and it does the same to the other person.
In short, be nice to your ex, if possible. Be friends with them, if possible. But keep it zipped: there are plenty of other pants parties you can be invited to.
It would hurt too much to go from meaning everything to each other to becoming a mere one night stand...
Thank you. That makes things muuuuch more straight-forward.