hey @David Donovan ,
you can achieve this by updating the flow status to 'On Completion' rather than 'success'.
For that select the flow arrow and right click on it and then select: Completion
But Completion expects it to atleast travel via that path and since your's is a case of either or:
meaning it would either travel via 1st path or 2nd path ; so there are 2 steps :
1) either create a duplicate web activity and use each one for the success or failure flow
2) have your main logic in 1 pipeline
Then create another pipeline :
P1 >> Web activity