do friendships disappear just because you're mad at each other

I've been pondering this question for a little bit now and I'm curious whether anyone else has an answer..

If person A is mad at friend B and becuase A is mad at B, they don't speak... is the friendship over?

Is it over if A is so mad at B that B no longer feels comfortable talking to A?
Is it over if A and B never resolve their difficulties?

What then comprises the nature of friendship...?

One might argue that it is the ability to rely upon each other. It is the ability to call up when in need. That it is the ability to chat when one wants to chat. One might argue that friendship is just some bond of goodwill between two people. (If A is mad at B, then is there still goodwill?) What if friendship is merely a misnomer for social association? "You are geographically close so I ssociate with you, thus you are my friend....?" That seems wrong. What if friendship is "you are culturally similar/mentally similar/ etc. ? In general, I supose I think of friendship as people caring for one another and being able and willing to express that... so it befuddles me when people are still friends and yet they are mad at each other and don't talk... Apparently I have even engaged in it... but I still don't quite understand.

Anyone have an explanation ?