Is this game pritty much over when all quests are done? Not that I'm even close to it yet and I still need to try alt and some books to read. Do some monsters respawn in dungeons or they all vanish from world?

Dungeons respawn.

You can keep getting quests from all the factions. It never ends.

Yeah you can play after the ending

Cheers

ES never ends.

Every video game has an end unless it has some sort of random system that creates every single instance a unique quest, landscape, etc. I believe Pac-Man was never ending, though i could be wrong.

You'll always get random quests, so there is always something to do. You can also "extend" the game a bit by self-imposing some rules for your character. For example, I only use smithing to upgrade items that I've found. I don't craft anything. This way, it will take a lot of time to find the "best" items for every slot, giving a purpose to on-going dungeon-diving.

The game ends only when you get bored.

Dragons respawn!! By Dragons I mean, like big world wall dragons!! 14 in game days for me.

Yes, but the PvP is unbalanced and raids only want you if you already have good gear and won't take any of the popular classes since you only need one of those per raid.
you could always grind dailies if you wanted, but that can get boring after a while.

Edit: oh wait, wrong forum.

You will, eventually, get to a point where the only quests available are the repeating quests you get from factions. This will take you a long time, and I mean a long time - to the point where it's far more likely you'll start another character before nailing all the quests.