I was going to ask how Janet van Dyne has survived 30 years in the quantum realm without food or water, but I assume there is probably some kind of answer in the special powers she seems to have gained from said realm, which allow her to heal others.
However, there still lies the question of why Hank would assume she was still alive after 30 years. After all, he didn't know anything about her ability to heal and/or survive until after he had gone deep to rescue her. They were all very surprised at the fact that she had gained these powers after they had already gone through the elaborate rescue mission.
So why would they assume that she might still be alive after 30 years?