with the genie, if your genie goes out (unplugged, disconnected, something like that) then your mini's will be out too, as they require ALL their information from the genie. if the genie is defective in some ways, its possible that the mini's may still work. if you have a standalone HD box or HDDVR from the H-XX or HR-XX then they will not be impacted if the genie goes out, simply if the satellite reception does. as far as watching D* on other devices, the GenieGo lets you watch material that is already recorded on your genie via streaming, or you can use it to download the recording to your device for offline viewing. to download recordings i believe your device has to be on the home network of your geniego (haven't tried VPNing though haha). you can also watch alot of the VOD and live TV content through the D* app, again via streaming.
apparently AT&T has a $200 (x12 months) bundle for 4x cell phones w/ 10 gig, internet, and D* (Genie +3 mini). sounds like a hell of a deal to me, but haven't read the fine print.