1) Is the Witcher 2 the only possible reward from the stamp collecting game?

2) Until the event is over, is it feasible to complete a second stamp set, or not?

It says "THE WITCHER 2 + THE GAMERS: DIRECTOR’S CUT FOR FREE" and not "WHATEVER YOU WANT FOR FREE", so... Yes!? Take a calender and count. November 18. you'll collect your seventh stamp and the sale ends on November 25.

19 - 1st stamp
20 - 2nd stamp
21 - 3rd stamp
22 - 4th stamp
23 - 5th stamp
24 - 6th stamp
25 - end of sale - no new stamp for you

You also get the movie "The Gamers: Director's Cut".

But besides that: Yes, "The Witcher 2" is the only game reward you'll get for collecting the stamps.

The blues have indicated that if you already own one or both of the stamp giveaway items, you will get a gift code for those items.

Maybe if you're real quick ;-)

Ok! That's good. Thanks!

Correction - you'll get a gift code for both items no matter if you already have them or not. ;)

edit: http://www.gog.com/forum/general/2014_drmfree_big_fall_sale_8b1f1/post356/