Transactional versus Merge Replication (Restore backup after downtime)
for backup purposes I would implement database mirroring. if read access is required then using database snapshots could help.

http://technet.microsoft.com/en-us/library/ms175511.aspx

i believe that merge replication would work to eliminate the need to backup/restore from B to A, but the performance penalty would be considerable. if the base is small then it would be fine.