None of the old non-is super telephoto lenses are on the CPS elgible for repair list, and haven't been for years. If you have a problem that requires parts, you might find a independent repair service who has a part thats new or salvaged for a very high price, you can be sure that the commonly replaced parts are in short supply already.
Its definitely a risk. It won't be worthless if it can't be repaired, the parts for salvage may make it valuable, maybe more than you are paying.
I'd look for the IS version, they will be repairing them for another 5 years or so.