Reproduction:

Running around on the map it is easy to want to check on quests, leading 
to pressing Ctrl+Q, which quits the game.

Happened to me twice within less than 2hrs of gameplay, leading to loss of 
many minutes.

New players (but who might be used to diablo etc) are likely to trigger 
this by accident and assume the game is unstable.

Solution:

There should either be a "do you really want to quit" or the command 
should be harder to trigger by accident (Ctrl+Alt+Q) or there should be an 
additional automatic autosave.

Indeed. However you can switch on auto-run.

You can change the keyboard binding for quitting.


Proposal 1 for game design:
 a) no change
 b) Default is set to Ctrl+Alt+Q
 c) Default is unset


Proposal 2 for game design:
 a) no change
 b) auto-save is done at quit
 c) another keybind is added that does quit+save

I suggest to change the default keybind to something more obscure, like OP suggested. This makes it unlikely to close the game by accident. Ctrl+Alt+Q is good.

It's obviously not good that a certain common key combination just closes the game without warning. This can totally look like a crash. I recently made a 1.0 playthrough and the game suddenly closed one time and I assumed it was a crash. MAYBE I just pressed Ctrl+Q because I sprint so often (but I am not 100% sure).