There was very little new root growth. A proper soil mix will allow for drainage while holding enough moisture for the plant without causing root rot, etc. If you are in doubt use the above mentioned 'General mix'. Bonsai nurseries now carry prepackaged bonsai soil which can be used as is, or modified for your specific trees. The Juniper is one of the most recognized bonsai specimens and is frequently the first bonsai purchase many newcomers make.
Junipers do make very fine bonsai.
Although they are not 'difficult' bonsai to manage, they are frequently 'mistreated' and therefore do not last long. Well, we hate to break the news to you, but, if you have a brown juniper, it is probably dead. The most common mistakes made with junipers are over watering AND lack of sufficient sunlight. Junipers are outdoor trees. If you have no way to grow them outside, find some nice person who knows about bonsai and can give them a good home.