If the direectory for archiving is full you will see lot of erros in alert.log saying that. You will free space in that directory and the database will continue normally.

If all your redo ogs are full and the directory for archiving is full, then the database will stopped, waiting for you to free space. sometimes I saw a database go down when the archiving is not possible and all your redo logs are full.

In relation to your last question, I think it is not possible to do that.

Hope this will help to solve your doubts

Angel