Whether a transaction is effective, if one of the parties didn't expect a condition [which triggered the deal] to be fulfilled: Eruvin 82a; Nedarim 27b
The above, where the parties formally agreed to carry out their obligations in the event that the condition would go through: Nedarim 27b
Whether such a transaction is effective, where a blocking-condition didn't come true and the unwilling party could have made it so [and didn't]: Nedarim 27b