You can't keep a good woman down. Case in point: Ellen Ripley. Even if she only survived two-and-three-quarters of the first three Alien films, the DNA in her blood cells was enough to create a pretty killer replica (which gives us all hope for future Chuck Norris clones, but I digress).
Ripley could have gone the way of Dr. Frank Poole a whole bunch of times throughout the series. As the only survivor of the Nostromo (not counting Jones the cat), Ripley still could have been torn to shreds when the alien hid out on her shuttle. In Aliens, Ripley and a few of her compatriots survived a tough battle with the Alien Queen aboard the Sulaco. Even a universe-saving suicide in Alien 3 barely slows Ripley down -- the follow-up isn't called Alien Resurrection for nothing. How does she do it? Our guess is those decades-long stasis naps do a body good.