A very important question, as I'm sure you've never heard before!

Even if I choose Helly to survive, she will intentionally fling herself onto the walrus's tusks to spite her outie. Helly gets walrused, without question.

I choose Dylan to live, I think. The walrus incident is inevitably going to cause a great deal of bereavement, but people are dependent on Dylan in a way they aren't with Mark or Irving, so I think his death is the one his loved ones would find hardest to survive.