I guess (but only guess) that with some very bad luck that could be true, but most likely it is just an urban legend. Sperm cells can stay able to connect into the egg cell for a few days, at least inside the woman. I really don't know about surviving on the floor. And maybe a quick movement from mouth to vagina wouldn't still be deadly for them.

But in the end, most of couples need months to start a preagnancy with normal conditions and normal ways to insert the sperm cells, the possibility for a succeed preagnancy isn't too big even then. And with this scenario, there is so many ways for the sperm cells to be damaged on their way..