Sorry. My keyboard doesn't work correctly. I typed adverb clause but i don't know what happened to it. Would you please tell me the reason why we can't use if here?
You can use "if", as in your first sentence. You can't use "If stopping ... " or "Stopping ...".
You can't say, Stopping, they risked ..." because they didn't stop.
You can say, "Stopping would place them at risk of ...."