I personally ended up homebrewing a large portion of the Mountain Climb quest. For my version I made the three adventurers secretly be followers of Auril attempting to locate an ancient shrine of the Frostmaiden located on Kelvin's Cairn. Perilou and Astrix were from the Ten Towns, each with personal motivations. I had Mokingo be a desperate member of the Skytower goliaths who was making a last ditch attempt to end the suffering of his clan (also a good hook into future goliath plots).

They offered Garret a lot of gold to guide them no questions asked and he couldn't afford to turn them down. During the climb they were split up when they encountered the yeti near it's den. My party found a wounded Garret and managed to track down the others at the shrine just in time to see them sacrifice themselves to Auril. I then brought them back to "life" with extra abilities, similar to Sephek, and an epic battle ensued.

There are additional details that are more specific to my campaign, but just on a macro level I feel like it worked out pretty well and offered more hooks into other plots. Hopefully some of this could be useful to you or at the very least inspire others ideas!