If your trip no longer serves its purpose because of the delay or cancellation, and you're no longer at your point of origin (for example, if you are at a connecting point), then the airline (large or small) must rebook you on a flight back to your point of origin that accommodates your travel needs, free of charge, …
Do airlines wait if connecting flight is delayed?
It varies. They will often wait a little while, especially if it's the last flight of the day and even moreso if there are multiple passengers making the same connection. I've had Delta wait for me after inbound connection delays on several occasions.