Resume-wise he can just not put the position on there, it's easily explained away by a break traveling/freelancing etc.
As for financially, I agree with you for the most part. I'd still rather take the hit on the money and get out ASAP, you can always earn more. The best situation would be another sign-on bonus that paid the original one off - as long as the new position was good enough to last the year.
But, if he's getting a $35k sign-on bonus he must have quite a good skillset and be earning a high salary wherever he lands. Paying it off will be unfortunate but is totally doable.