I've noticed that some quests disappear after a while. For example there is a quest east of Oxenfurt with a guy and a wyvern - I just noticed the quest marker and thought I'll do this quest later - as well as two quests south west in Novigrad (one where a woman was bothered by someone).

Is this disappearing connected to story or level progress?

They are probably timed.
I met a nilfgardian soldier being harassed by people. If you ignore him he gets killed without you having a role in the event.
If you get close Geralt starts talking to them and can intercede to save the soldier.

The ones you found are probably similar.

Ok thanks. One thing thats weird though is that I'm unable to find these quests now, even when loading older savegames (Just wanted to see for how long they were available). I'll check again tomorrow to confirm this.

I have that wyvern quest too. I still had it listed and so I went to do it (still in green letters). I talked to the guy (Hans, I think), but the quest didn't update. It still indicates that I should talk to the guy, but when I do he asks about progress. I found the area (I think) were the beast would be, but no sign of the monster. The patch seems to have broken the quest. I was hoping this new patch wouln't break anything, but nothing's perfect I suppose. I hope that they work out the bugs they've introduced with 1.07.