So I travelled all down the road from the docks picking every pickable plant I could find up to Solitude, I picked one particular spot to check (by the horse cart). Then I went to the Winking Skeever and stayed in the inn for 10 full days without leaving. What I discovered afterwards:
1. After 7 days the Tavern fella seemed to reset back to his bar position.
2. I told my Follower to wait and she vanished after about 6 days. Went home out of boredom I guess.
3. Plants did not respawn.
But it was mentioned that it could take up to 30 days, so back to the Tavern I went and stayed in there not for 30 days, but 40 days and nights!
The Taverner kept asking if I was sick- I sure was after that! What I discovered:
1. Don`t tell your Follower to wait and she`ll stay with you all the while.
2. The taverner resets to the bar every 3 and 7 days.
3. I went outside to check the plants and they HAD all RESPAWNED!
So worry not, Otheral, ingredients do respawn, your alchemy is not ruined, you only need be patient. I suspect everything else vanishes like the ash piles too after a time. If you want to test do as I did for the Xbox version, then go for it, but wait 30 days.
Many thanks to Pseran Wyrd as he is correct.

That`s one problem solved.
