You can spend your Etihad miles on any Etihad Airways flights or any partner airline they cooperate with including:
And many more
If you do not redeem your Etihad miles within 18 months they can expire, But there are many available flights and upgrades which they can be used on.
Yes! If you buy, sell, or spend any guest miles within the 18 month period, the expiration date on all remaining miles will be extended an additional 18 months for your convenience.
Not only can you use your guest miles for an upgrade on Etihad Airways, like an upgrade to business class, but you can also use them to shop on their online store, or convert them to cash with their card.