Once a unit is wiped out completely is it gone from he game for good or can you bring it back in by spending threat?
Defeated units and deploy/reinforce
You can reinforce that unit with threat as well. So if you have 3 Stormtroopers and 1 is killed, you can reinforce the lost figure for 2 points. If the unit is completely wiped out, however, you can make it reappear only if it is in your open groups, and yes, it costs threat.
The card for any group that is defeated goes back to your hand, and can be redeployed at the normal threat cost. This includes starting, reserve and open groups.
However unique units (i.e. Villains) that are defeated can't be redeployed in the same mission.
Any non-unique deployment card returns to your hand and can be deployed later on an optional deployment by paying the threat cost.
Reserved groups can only be deployed from the mission rules/events. But once deployed and defeated, they are just like any other deployment card.
Unique figures cannot be redeployed by any means after being defeated.
My understanding was that only Open Groups can be repurchased once defeated.
All the others are removed...
yet above Abyss and a1bert say otherwise?!?!
You start a mission with your hand consisting of Open Groups that were not deployed during special setup. All non-unique deployment cards return to your hand after their last figure is defeated. It does not matter whether they were initial, open, or reserved groups. There is no way and no reason to track that information. There are no rules that make a distinction between the original source of the groups.
Even if a group (usually one figure) gets some special abilities from mission rules, if that figure is defeated and is not unique (and it wasn't a end of mission condition to defeat that group), you can deploy that deployment card (without the special abilities) later.
It is also said explicitly in the rules:
When an initial or reserved group is defeated, except for
unique figures, the Deployment card is returned to the
Imperial player's hand and can be optionally deployed during
the Status Phase.