Hullo Hullo Playgrounders!

So, my character is a ninja, and he and the party's shadowdancer have decided to have a friendly little sparring match (and by that, I mean they are murderously enraged at each other, and are about to have a showdown).

The last session ended with the ninja standing outside a tavern in the street, with nothing around him, at about 5 o'clock; so he has a shadow, but there are no other shadows near him.

The shadowdancer is standing just inside the door to the tavern, so there are shadows a-plenty around him.

Now, a favorite technique of this shadowdancer is to jump into a shadow and out of his opponents shadow, surprising them, and getting all sorts of DM granted bonuses. So, I anticipate him jumping off to the side to get into a shadow, and trying to pop out of mine. Therefore, I left a note with the DM that specifies a readied action. "If he leaps for a shadow, then I use my Ki ability to turn invisible, rendering me shadow-less."

So, I know he won't be able to pop up next to me, but I don't know what exactly will happen. Will he still be able to enter the shadow, but lacking the exit be trapped on the shadow plane? Will it fail like a normal dimension door, as he takes 1D6 and gets shunted to a random shadow within 100 feet? Will the ability not work at all and he just cracks his head on the floor as he tries to dive into the "portal" that he can't set up, because the other end isn't there?

If anyone has any insight/other ideas, they would be appreciated.