vacancies under STV should be filled using countback method like Cambridge MA.

It doesn't matter who came "17th" in a 16 person election, it matters what the preferences of the voters who would be disenfranchised should the vacancy persist wanted

https://en.wikipedia.org/wiki/Issues_affecting_the_single_transferable_vote#Countback

If your bylaws don't specify that and leave it up to the other members of the committee, they can choose to use countback method

To make the subtweet a tweet: Members of DSA's NPC will be tempted to appoint 2 backfills from the SMC-B&R-CPN coalition. This would gain them precisely nothing except backlash and additional administrative work.

If you check the votes, I guarantee you'll find countback method would elect two LSC/Build/CC people who aren't Zac or Ravi. That seems... fine?

SMC-B&R-CPN are winning all the votes they are united on anyway. Why create the extra hassle?