But what would happen if either Kiva or Paypal failed? Where would the money go?
Hm... in the real, real, real doomsday scenario: Down the drain. (like always - there's always a scenario that would lead to a loss of anything)
But this is highly (!) unlikely to happen, and there are also certain precautions and safeguards in place AFAIK.
For example: Our funds are not administered by Kiva itself but by Kiva User Funds LLC (look at your receipts from Paypal or your CC company) - that means that our funds are separated from Kiva's budget and thus not in any danger to be drawn on in case of Kiva's default. Kiva User Funds LLC should have no creditors apart from us lenders, so that the funds are rather safe, there (apart from fraud scenarios, I guess).
A (IMHO incredibly unlikely) failure of Paypal would mean that any funds in your Paypal account are most likely lost (apart perhaps from government or inter-bank guarantees), but it would not affect the monies administered by Kiva/Kiva User Funds LLC - and Kiva would have to find another way to process payments and honour withdrawals.
Best wishes,
Wolfgang.