In Secret History Kelsier tells Vin she doesn't need to go to the beyond as she held a Shard. She agrees, but wants to go with Elend. So this means Danlinar doesn't HAVE to go to the beyond. Taravangian sees him stretch, and could just assume he is gone to the beyond. If this was Dalinar's POV saying he went there or something like that... then maybe...
For now, I do think some other shard took him somewhere and I am ready to see two dalinars clashing...