Does the certificate matter for TDE? Apparently not as I found a number of people discussing the fact that the expiration date for certificates is not checked for TDE restores. So if your certificate expires, you can still restore the TDE backup.
However the documentation doesn’t mention this, and I think it ought to be clarified, so I submitted this Connect item. Feel free to vote if you agree:
Whether the expiration date should matter is another debate. I think it should, but I need to really think about the pros and cons of this.