Sperm are alive and active as long as they are wet. If your partners' hands are still wet or damp, you could get pregnant. Sperm are very determined little creatures. Active sperm placed near the vagina can find their way into the body to fertilize the ovum. Pregnancy can and does happen this way.
Semen dries up when it is exposed to air. As it does, the sperm will be neutralized and die. Washing your hands with soap and water will also get rid of the active sperm. This would be a good practice to get into if you and your partner are going to engage in digital stimulation (fingering). Hand washing also helps prevent the spread of bacteria and other germs.
If you would like to see a response to a similar question, Click on Pregnant From Fingers After Masturbating.