I love this theory! I’m rereading Oathbringer now and the stormfather said that talenelot came back to join “the other 9 living heralds”.
If this theory is true, and I think it is, then either the stormfather doesn’t know that a herald died (doubtful) or he’s lying (which we apparently see in the SA 5 prologue.
Further, if the stormfather is lying about this, then this would seem to be the key piece of information regarding exactly what the heralds were “risking” by breaking the oath pact.