I think it's important to have a contingency plan. Now, here's a thing. Contingency plans cost effort. However, a risk, in itself, has the potential to cost the whole thing you're working on, so the effort of a contingency plan is worth it to cover a risk. But... if you're not sure what may or may not work, then you can't be sure that one particular plan is going to be totally worth pursuing. Should you be more cautious than throw effort at a potential unviable contingency plan? Is there a benefit in being more conservative?
I have been bothering people a bit recently with my approach, which is to have multiple plans running in parallel. You don't invest heavily in each plan, but you do investigate it and its sibling options a bit. What then happens is that you have a bunch of open options ready to use if you need them.
If you only have one possible plan and wait for it to fall through before generating an alternative, then the elapsed time is greater, and your options start to reduce the longer you wait. If you keep a few irons in the fire until you know more exactly what you need, then you're always much more likely to be able to do something.
So, it's apparently more effort, but you get a lot more in return.
Keep your options open!