...its not known where the Mage will go after the meet, possibly to the temple stronghold of the cult... which is close to the meet (that seems like the most likely destination but he may just head back to the Guest Embassy?)
If I know the mage is likely to return to the temple stronghold or the embassy I would have to conclude that taking him in the alleyway is the best option.
Since the bounty hunter knows about the mage's client, I like jdale's idea of interception and impersonation of the client. That removes a potential witness/combatant from the coming confrontation. We still need to capture the mage though, as I'm sure if his "client" just happens to ask, "Hey, about this other mage that I heard was kidnapped?", that wouldn't go well.
So I'm a bounty hunter (literally a RM bounty hunter profession? Not just my, uh, profession?) and I have two sneaky allies in a thief and burglar? And I have a heavy crossbow and weighted net.
This is what I would do if I was feeling a bit crazy!
Whoever between the thief and the burglar has the best acting and or disguise impersonates the client. Let's pretend it's the thief. If I was lucky enough to have acquired the kregora manacles then the theif will carry those. If no kregora, then he will carry normal manacles, rope, ball gag and blindfold. The thief will have their normal weapon hidden on them also. Being a thief I would hope they are something easily concealable like a short sword and daggers. He will also have a healing potion handy.
Now for the burglar. I want him with the weighted net. Ideally, I'd love to get him hidden in the alley before the meeting. I want him to be able to get that net on the target as easily as possible.
If I'm the bounty hunter then I probably have the best weapon skills, so I'll take the heavy crossbow. I'll want to be hidden on a roof over the alley if it is not too high. I'll have a rope secured that I can slide down into the alley after I take my shot.
Now for the crazy fun part! The GM would expect me to use the crossbow on the body guard and the net on the mage. No!
Hilarity ensues when I snip the mage. Bolted! How often I do I get a one shot one kill? Not bloody often. But a mage who is stunned and bleeding and suffering high would penalties isn't teleporting out or fire-
bolting us.
Simultaneously, the burglar drops the net on the bodyguard. If that works he will be easy to eliminate after I slide down into the alley next round and the burglar subdues him. If I was feeling foolish and sentimental I would explain to the bodyguard that he has already failed, and his only choice is to die for the mage or sit this one out. If I wasn't an idiot I would realize I could never trust him to run to the mage's allies as soon I release him. The burglar and I begin stabbing through the net. What's the bonus for attacking doomed men stuck in a net? The Prone bonus (+50) might be a bit much, but I bet it's pretty good.
Meanwhile, assuming the mage is alive but in very bad shape, the thief secures him with the kregora manacle or the more mundane items if necessary. If the crossbow bolt didn't do the trick then the thief would have acted immediately with a followup attack.
If all goes according to plan (yeah, right), the mage should be secured and the bodyguard dead by the end of round two or three. The thief can administer the healing potion before the bleeding gets out of hand.
Surely, we wouldn't have done this if we didn't have some sort of safe house nearby? Getting the mage out of the alley and into the safe house might be tricky. I've always liked having a horse and cart parked nearby with a tarp and other goods in the back. We would then drag the mage into the back of the cart and place him under the tarp along with the thief, who keeps a dagger on him.
Once in the safe house the mage knows we're serious. The interrogation begins.
Granted it would be a terrible time for that lucky 100 on the "E" Puncture critical table.