No, dentures will not fall out if they are properly fitted and cared for.
If you have concerns about your teeth falling out, you might consider using an adhesive or getting implants.
Years ago there were frequent problems with lower dentures. That is because lowers just rest on your jaw and there is no suction. You have to learn to hold them in.
Today many people are having implants placed in their lower jaw. Their teeth securely snap onto their implants. They can speak, eat, and smile confidently. It’s a game changer.