I am new to the game myself but I here's how I understood it:
1) Sounds like you have it down. You can play a red/yellow action card for a race you do not own the destiny card for but then it will be discarded. This means that you will not be able to "bet" with it in round 7's Destiny phase.
2)No, The piece remains in the territory it attacked from.
You're right on both answers.