The ladybugs lay their eggs on the undersides of plants and leaves, then 3 weeks later the larvae and pupa emerge for a new generation.
We have loads of weeds, bushes, trees and a creek so the chances of them moving on for us is pretty slim. Normally they will go where there is food and water, so if you have a garden in the burbs with little vegetation around then they might leave for other food sources.
I generally don't have an issue with them getting in the house, but if I find one I just toss it outside again.