Reneging external offer

I interviewed with a company through WW but they ended up giving me an offer externally instead of through the WW match process. I still have a few interviews coming up and im waiting to see if I get matched with any internal jobs. If I accept this external offer now and later get matched with a WW position that I would rather take what happens if I back out of the external offer? Has anyone been in a similar situation and are there any consequences from Waterloo?