Period is due in a couple days. Had sex but condom slipped off and didnt realize until we stopped. Is pregnancy possible? How likley? This period miss?

Pregnancy? Theoretically it is possible but it all depends on did the semen actually go in?Around what time in your cycle this mishap happened? If it happened around your mid cycle and days after. ,the likelihood is more. But you have not even missed the period yet. If you miss your period then get a pregnancy test done.
Don't know timing? Pregnancy is possible. Did you just have sex? If you have sex a couple days before period is due, that it is not a particularly fertile time. If you have sex closer to 14 days prior to anticipated period - that is a higher risk time.