If they're not adopted, chances are they will die before they're surrendered. A lot of petshops don't have long term accommodations. Most of the cages you see are way too small. A lot of animals just give up. Then die. And when they die, off to the dump they go. Which is the legal way to dispose of dead animals. They're considered waste.

That being said, not all petshops and rescues were created equal. A lot of petshops are actually ethical and take good care of their animals (that they get from a reputable rescue). While a lot of rescues don't.

Before adopting from a rescue, you should look into what the process to become a volunteer or foster parent is. Are they training you? What questions are they asking? A lot of places just ask you if you've had this type of animal before and don't test you on anything nor visit your home to make sure it's adequate. If they don't have fosters, visit their installations. Is it clean? Do you see their volunteers handling the animals correctly? Do they seem to know what they are doing or do they have the "I'm a rescue, I can do no evil" mentality? If they use "but we're just a rescue, we're doing our best" excuse, walk away.