[PeteF]

Based on my experience, the risk question has two factors. First there is the probability of a failure, then the criticality of the failure. From your photo the cross sectional area of the stud does not appear to be compromised to the point of being the current-limiting area, so that would make the probability factor low. But, IF the stud is compromised where you can't see it, and you judge the criticality of another failure as moderate or high (fire potential), then the risk would be moderate/high. Lastly the time/effort/cost is not unreasonable, so I would replace the alternator. You'll feel much better when far from home. My 2 cents.