LEAVING UK - need to bring my biometrics residence card?

Hello,

I have quite a complicated Tier 4 student visa application. I am applying for a new student visa because my college has recently got there sponsorship licence. The university that I applied for my current visa is an affiliated university that's how I got my visa but now they are requesting I change the visa to my college sponsor licence. Anway this visa is valid until 2012 but I am making a in person application on Wed.

I understand that the biometric residence card is issued within 7 working days. My question is, can I leave the UK with just my passport? Are there any problems with immigration? Do I need to show my biometrics card? Even though my passport has another valid visa on it? I am thinking of getting a friend to mail me the biometric residence card when it arrives so that I will have it when i return to UK? Will that work?

Thanks for any replies!