The sun in TES lore is a portal to Aetherius whence all of Nirn's magical properties are derived. Maybe that's where the Dwemer went...
No, but it is why the sun-symbol is prominent in Dwemer mythology.
The sun represents the departure of Magnus from the mortal plane.
The Dwemer, like most elves, see Creation as a trap and not as a gift and seek to escape it.
The sun symbolises this.