"You die at first light!" -- 101 reasons not to kill captive PCs straight away

[Razjah]

45. The enemies want to turn them (lycanthrope, vampire, curse, etc.) so they need them alive.

46. If no one returns with horror stories, how is the monster supposed to improve its horrifying reputation. One will be selected to be sent back after watching the rest of the party be killed.

47. The villain is having doubts about sending them to the BBEG (Vader and Luke) so he/she is stalling for a day or two in hopes that the questioning is helpful.

 

[darjr]

48. Turns out the bad guys are the good guys and the PC's have been working for the bad guys all along. The good guys are merciful.

 

[Electric Wizard]

49. Captors have qualms against capitol punishment. Those sentenced to death are led to the top of a mountain, where they are chained to the rocks and left to die of exposure.

50. The executioner has the flu.

51. Falsely believes the PC's are well-connected to wealthy and dangerous people. The captors provide decent accommodations and prepare ransom letters.

 

[Bluenose]

52. I'm a practical sort of guy. If I kill every group of prisoners I get, pretty soon no-one will surrender to me. So I sell some to the galleys, put some to work in the mines and quarries, and eventually the ransoms come in. And best of all, when I surrender I can expect to survive, or my names not Boldrok the Indescribably Vicious.

 

[hopeless]

53) This overlord gives them the option of either dying horribly or dining with him and his troops for that evening and if they agree he willingly releases them as long as they return to their home city with a message about a truce and a trade agreement since an army does march on their stomachs and building ties with the neighbourhood cities rather than looting them is a fair trade in return for the supplies and goods they can buy in return for all of the loot they have gathered so far.
However the city might have other ideas especially the ones that don't realise they have absolutely no hope of fending off the inevitable conquest if they refuse.
Of course this assumes the big bad is just one of many but this give the PCs the chance to earn their stripes as heroes by negotiating a truce that saves their home and countless lives that would have been lost in the pointless war that would have followed and in return the PCs have an ally they can call upon for aid when they discover the other big bads...

54) A necromancer wants them as additions to their army however they don;t just want to turn them into plain old undead they want to modify them into a suitable improvement which requires they undergo a test of their suitability which involves letting them loose in their predecessors secret laboratory unaware that sometimes death isn't the worst thing that could happen to a PC!

 

[Sunseeker]

55: Victory is X^nth more satisfying when the world sees the heroes have failed and said heros much watch the world burn.

56: Your sexy assistant pleads for you to spare them in exchange for...indulgences.*
*note to self: kill sexy assistant first.

57: You actually lack the power to kill the heroes...but SHHHH!!!! don't tell them that!

58: Getting them to see your point of view, that your evil, terrible scheme to murder millions is a better result than the world destroying itsself.**
**as a nice side-perk, it's so very satisfying to not just break the heroes body, spirit and mind, but to twist them in to accepting yours.

59: You're an egotistical maniac who is very, very un-genre savvy.

 

[Zireael]

60) You put them to a test in withstanding a devilish torture machine.
61) You need them as translators, having first ensured via truth magic that they will translate correctly.

 

[Kaodi]

62. You are not really the BBEG and you are wise enough to be able to admit it. In fact, if the BBEG wins it would probably work out badly for you. So you propose the following: You will moderate some of your more despicable tendencies if the heroes agree to go on what is practically a suicide mission to take out the BBEG. You will even lend then material assistance, but you will also place a powerful curse on them such that if they should betray and attack you they will be sapped of enough power to make it impossible to overcome the BBEG. Of course, if they defeat the BBEG without all dying they might come back to defeat you later, but you like the odds on that better than if you leave the BBEG to further his own plans uninterrupted.

 

[Dannyalcatraz]

63) the BBEG is a long-lost friend or family member of one of the members of the party

64) the BBEG thinks someone in the party is HAWT, and plans to take that person as a consort. Consider Ming the Merciless from Flash Gordon or a twisted version of the Cinderella story.

 

[Scott DeWar]

I thought cinderella was twisted enough when the step sister chopped off toes to try and wear the glass slipper, not to mention the prince wanting to marry such a young girl-a coal minor named CINDER ella.