I've a slightly different slant to Noajthan.
ngolan62 wrote:1. Does she need to get it renewed? Does she really need it?
You replace it by an RC. I believe one should get a further one before it expires, so your wife always has a current residence card. However, that process might have pitfalls I am unaware of.
If you own your home and your wife is a lady of leisure, i.e. does not work for anyone, then no. Otherwise, she needs it. For example, she needs to show it at her rent-to-work check if you are in typical privately rented accommodation, unless your landlord is just going to report her as a suspected illegal immigrant. (I haven't heard that that loophole is going to be closed down.)
ngolan62 wrote:2. How do you renew an EEA Family Permit? Nothing is clear about that on the UK.Gov website.
See above.
ngolan62 wrote:3. If she doesn't need an EEA Family Permit, what happens when she travels back to the UK without one?
If she doesn't have a family permit or a residence card, she'll need your marriage certificate, evidence that you are a worker (or a student with comprehensive sickness insurance for the two of you, or self-sufficient), and your telephone number so it can be confirmed that she will be joining you. In short, hassle. If she lacks the documents, she may be held until you come to the port with them. In the worst case, she will be refused entry.