I let the car overheat after most of the coolant came out of the cracked reservoir cap. Now, when i run the car, coolant comes pouring out from where the head and block meet. Do i need a new head gasket or is the head warped?

 

I'm not a seasoned Mini mechanic but since no-one else has replied;
I think, If there is a detectable leak at the head gasket, I imagine it would be prudent to remove the head and have it checked by a machine shop to ensure that the head isn't warped.
The same might be true to inspect the block at the same time.
Hopefully the the head hasn't deformed and is salvageable. But you're going to have to remove it (and check it) anyway in preparation for a head gasket replacement.

My apologies if I seem to be stating the obvious.

I wish you the best of luck.