I spoke too soon...
I just completed the Christmas bonus mission, and the Barbecue bonus mission just showed up again.
I'm glad it isn't gone. The previous bonus mission was, for me, the highlight of the Steam Summer Event, and this new mission is also quite fun, even if simpler.
There's something about these crazy bonus missions that just appeals to me. Probably the idea of American/British/French/German/Japanese/... soldiers fighting alongside during WWII, either to steal some meat and beer for a barbecue, or to defend a Christmas tree from evil snowmen and a crazy scientist bent on world domination, dress up as Santa Claus.
I would gladly pay for a DLC pack with a few more crazy missions like these!