For those items that you mention there, it would be cost prohibitive to replace the entire unit. Keep in mind, most of the newer toilets do not include the best seats either.
Chains are easy to swap out as are the seats.
Happy DIY'ing.
If you are leaving the house, you definitely want to shut the water off to the house, in case the water line bursts. Otherwise, if you can find the frozen area, you can take a hair dryer to the spot to slowly thaw the pipes. Don't het the pipe quickly, as this will most likely cause the pipe to burst. Just always be ready to shut the water off to the entire house and have a bucket near. Good Luck.