As far as the future goes, I suspect that if/when Bliz or SC ever shuts down, one of the last things they’d do is code the DRM out of the client so that it could be used without a connection to the servers.
For the present, the DRM is one of the anti piracy/hacking measures, so it’s not likely going anywhere. The hard part is striking a balance between not inconveniencing customers and protecting IP.