Take a look at the branches...are they green. Take your finger nail and scrape off a bit from a branch(if brown or a non-green color) or the trunk and see if there is green underneath. I have a Tarrocco blood orange that was affected by the cold (20 deg. and I didn't protect it)but it still have some green branches(and many brown ones...no leaves of course) so I'm waiting to see what happens, and there's a branch leafing out but it seems to be a water sprout coming from below the graft. At least that's a good sign that something is still alive.

Since you've had it for years, I's say it's worth waiting for if you see any signs of life. One thing I did for all my citrus was water them with B-1 (or use Superthrive) ...first they suffered from the hot summer, then the cold winter...it seemed like the genteel thing to do.

jc