I'm with NickB on this one. The purpose of earning status is to enjoy it. Why get to that stage and then try to earn additional status elsewhere, while losing out on the benefits you've earned with BA!? Nothing will be 'lost' if you don't earn enough points to achieve Gold. You'll still earn double Avios and get the benefits of lounge access, fast track security, priority boarding, additional luggage, etc etc.

Also worth considering that if you're not going to earn enough points to get to Gold, will you really earn enough points with another alliance to achieve their equivalent to Silver, while still maintaining BA Silver...?