What if none of that is happening?
I waited now 3 days, and no sign of Lydia. I fast travelled to many usual places like Solitude or Whiterun. Also, I tried to get another follower, so I know that I still have one. I tried Lydia back at the Dragonsreach, no sign of her. I just remember that maybe last time i saw her was when i went up mountain to see the Greybeards. There is unfortunately only one verry windy path to there and I think i read somewhere that followers can't jump or won't follow up or down some tough terrain. So if she's lost on the path there, I thought I'd make it easy and transport up there near Greybeards hold or down at the base of the mountain in that town.
But no dice.
So now I wonder if perhaps I have a quest started that requires me to meet my new temp companion, in which case I guess Lydia was temporarily removed as mine and is waiting. But in that case, would she not act as if dismissed? and go back to Dragonsreach?
any input?
Do you remember where you last were with her? This happened to me with J'zargo. I took him with me on a mission in a Dwemer ruin. I thought I had lost him and then I was ambushed by Falmers. After I dispatched them I moved on, hoping that J'zargo would catch up, but he never did. So, I left the ruin, got Vorstag, went back and re-traced my steps. Sure enough, there was poor, poor J'zargo, a dead cat. I was heartbroken and I couldn't just leave him there... so well, I resurrected him. LOL After I rezzed him, he said something like. "You hurt J'zargo too much, I will cannot travel with you anymore." LOL
The followers shouldn't have any issues climbing the 7000 steps up to High Hrothgar. I took Vorstag up there and he made it without issues.
If you won't find her body and she won't come back to you, I guess you just have to let her go. Are you able to take a new companion?