Seriously thought about taking the deal but decided against it. These are SD's oldest cities including the first barb city he flipped, his military is lower than ours, and most importantly I'm last to play this turn so I can declare immediately and move in and recapture our cities before he gets any whipped units out.
However the cost would still be very high, it's doubtful how well we can hold his cities, and most importantly it would take SD out of contention and I want a strong SD until Magic and Dreylin are brought down. So while it would be a most amusing twist to the game, I believe it would ruin our win chances and so is not worth it. But if it were Magic making a similar offer, I'd absolutely have gone for it.
However the cost would still be very high, it's doubtful how well we can hold his cities, and most importantly it would take SD out of contention and I want a strong SD until Magic and Dreylin are brought down. So while it would be a most amusing twist to the game, I believe it would ruin our win chances and so is not worth it. But if it were Magic making a similar offer, I'd absolutely have gone for it.