It's obvious. They'll make up excuses to deny the significance of it. If they can deny it happened they'll do that. If they can use any artificial elements in the process to insist that it means nothing they'll do that. Or maybe other excuses that I haven't thought of.
If they absolutely have no excuse that even they can accept (and for many that's a very low threshold indeed !) they'll come up with something. Maybe they'll insist that apes are degenerate humans. It doesn't make sense in light of the fossil record but few YECs would care about that.