wait so by the author confirming dooshik can’t swim, does that mean they actually did di...

Yep :’)

son of a fucking gun T-T

We knew that already though. He almost drowned in the very beginning of the story and Jooha saved him so in my mind he did it this time, too! :'(

My guess is that they both died in that frozen lake unless Jooha saved him like in the past. I highly doubt it cause both were sinking at the end.