Also Xykon would be resistant but not immune persay. The Draketooths would likely fall, but with a tactical explosion of the gate they could take him out after a major attrition with...well...everything possible. They have high-end illusionists, and may well have a few low-Epics if the "go out and have kids" bit is more intense than we think and involves them raiding keeps and felling the White Dragon of Reddragonsville and the like.
In general, this scenario probably screws over everyone, killing probably half the party or more, obliterating Azure City due to the unraveling political situation (no Shojo or Hinjo along with a massive hole in reality), and leaving Xykon nearly unopposed as he plots. The only possible upside is that the Draketooths never get hit by Familicide, which leaves them as basically the last hope aside from "magic rock falls, Xykon and Redcloak die". Also, even if they do fail for whatever reason, TDO is still left unrecruited and leads to further continuation of the cycle.