Alive Off Payoffs

Key Alive Off Payoffs in Payoff Policy refers to an optional set of OFF payoff valuations - represented as an object of type KeySet - that are meant to stay "alive" (i.e. the payoffs remain due for valuation and settlement) after an event of a particular type is triggered provided the claims to such payoffs have been established but their corresponding payoff amounts have not been valuated prior to that event.
Note, the OFF payoffs are those associated with the key Off Pmt Fn of the various Contingent Claim objects.
In effect, the entry here introduces an exception to the default rule applying to all policies whereby the occurrence of any event causes the deactivation of all subsequent claims and all subsequent payoff valuations.

In more formal terms, it defines an optional mapping that is similar to that in Alive On Payoffs with the difference being that the entry here defines the effect that the occurrence of an event has on subsequent OFF payoff valuations rather than on subsequent ON payoff valuations.
For more details look at the description of the latter.