Söderström would have been good for this situation.
Internal replacement, is it Szuber yet? Would not want to pull him up too early, and it is so early in the season, but could see getting him up for a game or two while a long-term replacement is sorted out. He's played 1 NHL game so far.
Maybe sign Scandella or Shattenkirk. I don't know if Klingberg has recovered from his surgery, but if timing was right, could see that being a good fit due to him wanting a short contract to show he's back and only needing him to step in this year.