Well, it had better be fixed in time for the duathlon in September. The scheduling is complicated by being in Paris for most of next week. I'll try not to spoil the holiday by owrrying about it :(
If I'm replacing the crankset/chainset/chainweels (?!) as well, maybe I should get one with an external bearing race, which afaict is intended to stop this sort off thing happening. I know that Shimano freehubs have external bearing races for this reason, for instance. Looks like some entry-level Truvativ XC crankset have external bearings now--- my current cranks are Truvativ, although I'd have to locate and dig through the pile of paper that came with the bike to figure out exactly what the model name was. Says "FiveD" on the crank itself, I guess that's last year's model name though. Otoh, getting a replacement PowerSpline set will be much cheaper. Perhaps I should get a second opinion on whether riding it home with the crank coming off has damaged the spline surfaces.