Does this chainring need to be replaced?
Presumably with 12K+ km, and never having bought new chain rings, you have a very high cadence.  You should get a new chain every time you change your cassette, btw.  

If you are doing the work yourself, I don't see any reason to change the chain ring immediately.  Try the new cassette and chain and see how it works.  If it isn't broke, don't fix it. If it doesn't ride well after changing the first set of parts then yes, change it.

On the other hand, if you are taking it to a shop and paying for the work, it's probably worth having them put on a new chain ring while they've got it in the stand.  A good shop will test ride it and be able to tell you if it is needed before you buy.

12K is a lot of distance for the equipment, so I wouldn't hesitate to change it either way.