If the Primary cluster is down, will there be a data loss? If so can it be recovered from the secondary cluster?
Any committed data won't be lost. In Eon mode, a transaction is only committed when all the data of the transaction have been written to communal storage. Communal Storage is the single version of the truth in the cluster. Any new cluster you might revive from that communal storage will be up to date.
Exception is the data of any uncommitted transaction under way in the cluster going down, of course.