Could you have placed the other teleporter in a chest, or something?

It will be a while before you are you close to entering the castle, but if you bring the teleporter with you then, it will by 'borrowed' and you will get them both back later.

You can place the teleporter stone you have in a barrel, or something, and download a replacement set;
Lost Items - guide and directory of inventory files


The sapphire key was probably for a chest or door near where you found it. You may have lockpicked what it was for before finding the key. I dropped about half a dozen keys before beginning the blessing ceremony, that I had accumulated this way (pretty sure I didn't miss whatever they were for).

The thugs are not involved in anything else, so you can kill them for the better experience.

The cat you can 'talk' to should stay in Aleroth. If you didn't clear the orcs out from around Aleroth, one may have wandered in, or the cat wandered out...