Indeed they can cancel it, however you still have 30 days before it would expire, time enough to start your new job and get your visa renewed. As to whether or not they would give you a letter of release, don't they have to legally if they cancel your visa?
TDM sponsered my visa and they can cancel it if they want to and I would have to go to HK and take my chances comming back on an F visa.I would never let someone hold my visa and passport for any reason.They could make things hard for me but its cool now,as I will have a new job in aug.
I just got an offer for 11,000 at a school in the south so I don't care about TDM anymore......................Stay away from that place!!!!!!!!!!!!