I think I may have killed the elf in Stillwater cant find him anywhere I cant get the Stillwater giant quest nor can I get the amulet do I have to start all over again or can I just finish the game without these quests?

If he is dead but his (Myrth's) body is around (probably not if you don't remember killing him) you can cast conjure spirit and speak to his spirit about where Qintarra is. If that doesn't work, and you don't know what you would have done with the amulet... then you can force the pass through the mountains to appear, but it may break the game.

Go to these coordinates (there are West-South coordinates on the map panel as you move your mouse around the screen): 1288W 713S
You should be able to find Hardin's Pass, which if you go through it to the other side will allow you to explore the Glimmering Forest, and go to the coordinates: 1545W 656S which is where Qintarra is.

Like I said, it may actually break the game, because it won't update that you are supposed to be in Qintarra. I don't know if you have the Unofficial Patch and if that patch actually fixed the issue or not. But it might be worth a try.

Just a note, if you find his body but can't conjure his spirit, you can return his amulet to the herbalist in Shrouded Hills, and she will provide you with the location.

Not to condescend but I should mention it, are you absolutely sure you've checked his house? It's the furthest to the Northeast, prior to the path that leads to Hippington's house.