It is possible, because there may be some seepage even if the male does not fully ejaculate. It's better to be safe and use protection.
No, However she can never be sure that some sperm did not make it out of the penis while it was in her. This can hapen with out any one noticing.
Most often by artificial insemination. However, he may try to withdraw in time, but may fail to do so. Of course, even if he does, you can still get pregnant.
That is how reproduction works. There is no gaurentee that it will cause pregnancy, but that is how everyone in the entire human race was conceived.
Yes