I called Prosper before committing more than $5K to ask about their viability and what the contingency plans were if they were to fail as a company. I was told they have a standing agreement in place with a loan servicer that would pick up the existing (legacy) book and service them until maturity. I suspect we would lose all/most of the fancy stats and tracking mechanisms for our portfolio, but "our" notes are protected from bankruptcy. Any other thoughts or views on that topic?
Calling them and asking is not the most assured method.
Yes, they say they have an arrangement in place with someone to service the loans if they croak. However, they have said lots of things in the past that turned out to not quite be true, so you should interpret their statement more like "They
believe they have an arrangement in place, and it will
probably work." However, given the way they have changed their interpretation of contractual obligations in the past, you would have to conclude that management is pretty loose with their obligations to lenders. There is no certainty here.
On the subject of "protected from bankruptcy", that is certainly wrong. Did they really tell you that the notes were "protected from bankruptcy"

Read the prospectus. The notes they sell you are unsecured debt of Prosper, and rank equally with other debt. They are
not protected from bankruptcy of prosper.
The only protection you get from bankruptcy is the weight of the notes and the associated loans. If the amount lent on those loans, and therefore the amount of the notes, is substantially larger than Prosper's other debt, then the bankruptcy judge would surely steer most of the available funds to Prosper's note holders (ie you).
A bankruptcy judge would surely assign a trustee to make the loans get serviced somehow, so it does seem likely that the loans would be serviced.