Would a guy intentionally leave his penis inside a woman's vagina with a condom on after he ejaculates to get her pregnant?

That's a rather general question, but yes, it is possible that a man would do that if he had some reason for wanting the said girl to have his child. However, the girl will only get pregnant if the semen escapes from the condom, either because it has partly come off, or because it has split. The girl could take the morning after pill if she was worried about becoming pregnant, although this is not recommended as a regular form of contraception - it is for emergencies only! There are two reasons to wear a condom--to prevent pregnancy and to prevent disease. If you're TRYING to get someone pregnant while you've got a rubber on, and you're not creative enough to poke holes in the end of the rubber or to slip it off during insertion into the vagina, you don't need any children.