Indeed, you don't even need €50 for the pack; you can get it for ~€45. Of course, if you still don't want to pay that amount, you can wait some more, but don't hold your breath, as I don't see much chance for such a promo happening in the near future.
with 50 € you can easily buy all of them and they worth it :)
I think no one can tell, when these will be on sale again, beside of GOG, and they will not tell anyone.
Truth be told, I think even they can't. The publisher needs to approve of a promo of their games, and I guess not even the GOG staff knows when they can expect such an approval from Atari/Hasbro.