Hi.
Let me see if I can answer your questions one at a time.
Albatros wrote:...is it possible to get the hue lights to the last known state from Indigo when the power has been off and comes on again.
No. There might be some rather complex triggers that could be used to save various device states then restore them, but designing that would probably be rather tedious.
Albatros wrote:...is it possible for Indigo to know if the hue hub has been down so you can trigger form Indigo some actions.
Yes, sort of. If you enable the SQL Logger plugin (which is included with Indigo), you could create a trigger to execute whenever any Hue Lights Error appears in the Indigo log. This isn't quite the same as detecting whether the Hue hub is down, but Hue Lights Error log entries are pretty rare and usually only appear if there's a problem communicating with the Hue hub. If you used that as a trigger, you'd need to use some kind of condition in the trigger to prevent it from firing over and over again after the first error appeared, though, because the Hue Lights plugin shows an error every 4 seconds or so if it completely looses contact with the hub.
Albatros wrote:Or get notified when bulbs have goe offline
Yes. However, bulbs only show as "disconnected" if the Hue hub itself reports that the bulb is having communication problems. So, if the Hue Lights plugin can't even connect to the Hue hub, it won't change the sate of every bulb to "disconnected" because it's not the bulb that's disconnected, it's the hub. Granted, if the hub is not reachable, neither is the bulb (at least from an Indigo perspective), but the Hue Lights plugin is intended to just be a kind of conduit between Indigo and the Hue hub, so it tries to only show changes in Hue devices if those changes come directly from the Hue hub itself.
Ultimately, there isn't an easy solution to the scenario you're talking about. Lost Hue hub connectivity could potentially be included in the Hue Lights plugin in the future. As you might imagine, just from trying to find a solution yourself, it can get complicated and isn't something that can be added quickly.