If he’s Israeli/American, he’ll be the first to die under torture...sorry to say.
The exposed presence of these guys in Aleppo is valuable to Russia claims of western involvement with radical IS militias, so they will probably be involved in their detention
Israeli involvement with the islamic militants should also be a valuable tool for Assad to use to discredit them
Nothing bad will happen to,these guys as long as they can be sold back to,their governments in exchange for certain .... concessions and considerations ... To Assad and Putin
In fact, returning these guys eventually, well fed and treated, in warm fuzzy blankets and slippers could be a PR win for the “ evil tyrant” Assad