I'm sorry. I say hang on and hope for the best. It sounds like you've done what you can do far.

As long as the wood stays green, you have a chance... don't give up hope yet! As Laura has said, you've done what you can.

Root rot isn't a death sentence for a citrus tree. It is curable. I've done it (well with a lot of prayers too). Clip off any black root tips (where it looks like the anchor root has completely rotted off except for the tip which is black) and also any darkened feeder roots. Finally, remove any rotted detached roots from the root system. Next wash off any soil from the roots with garden hose. Next make a solution of 20% chlorine bleach and 80% water put it in a bucket deep enough to to contain the entire root ball for 15-20 minutes. Finally, rinse off the root system with water and replant in different soil. It's very important that you do not use the same soil because root rot is a type of fungus and can persist in the soil for long periods of time and simply re-infect your roots if you put it in the same soil. This process worked for me. Your leaves may all fall off after the process but as long as the tree is green it has life and will re-grow. I hope this helps.

Look into grow scripts Citrus tree care products they have a video on YouTube where they bring back a orange tree that looks like yours.