Once rabies symptoms appear it is generally considered beyond the window for treatment, at least in humans (see: http://www.cdc.gov/rabies/symptoms/index.html).
As ab2 said in their answer, if you have a gun and know how to use it you could kill the animal, putting it out of its misery. For humans who are 'past the point of no return' the treatment is more about minimizing the agony, and for animals in the wild maybe this is the best we can do for them and other creatures who may suffer from their madness.
Unless you are immediately threatened however, I think the answer is to let them be and increase cautiousness. Progress with heightened awareness and warn others as the animal will wander mindlessly and may have infected other creatures in the area as well. This answer is supported by the following link http://www.dec.ny.gov/animals/32131.html which states:
What should I do if I see an animal that appears to be rabid?
Stay away from any animal that's acting strangely, and let your neighbors know about its presence in the area. We do not recommend approaching it with a baseball bat or other club because that would require close contact. Sometimes your local police can come out and shoot it; however, even a sick animal will often wander off by the time outside help can get there. If it does have rabies and has wandered off, it will probably die within seven days, but it might have bitten other animals in the area, so it's a good idea to stay on guard.
Bottom line is: avoid rather than engage unless engaging has adds very little risk, and proceed with caution in any case. Notify others for their safety. If you might have encountered infection, seriously consider seeking treatment, as waiting for symptoms to show up is waiting too long and may be past the point of no return.
