help please re employment bond

my son was employed at a BPO in november 2011. he signed an employment contract which included a 100thou employment bond for one year. he left the company after three weeks dahil di nya nakayanan ang work, stressed sya masyado dahil sa higpit ng requirements nila. he did not resign formally, basta di na lang sya pumasok, nag AWOL po. after a month, the BPO sent him a letter asking for an explanation in 48 hours why he went AWOL. he sent an email (and hard copy) citing the trauma he went through and that he will not be able to return to work anymore because of this. the BPO then sent a termination letter kasi late na daw nag reply ang anak ko.

last week the BPO through its legal department sent a demand letter asking my son to pay the 100thou bond plus around 7thousand more for other cash advances that my son received from them and threatening to sue him if he doesn't comply in 10 days. my questions:

1. may nabalitaan na po ba kayo under the same circumstances na itinuloy ito sa korte?
2. may pwede ba legal remedy dito? kung papayagan ito ng korte di ba napaka-unfair naman because they terminated my son and he was just a probationary employee at the time?
3. would a letter of appeal do? should he send this appeal within the 10-day period?

i need your thoughts on this. thanks

i'd say he is liable for cash advances and damages for resignation without notice.

but the bond for 100k, in my opinon, is not lawful.