Note: this question can apply to any version. I just chose an end-of-life (and therefore in the past) one in the example to avoid "one can't predict the future"-type answers.
The example, to make the question clearer: if I had kept running
sudo apt-get install <specific-package>=<specific-version> && sudo apt-get remove <specific-package> on my Ubuntu once a day for the last 5 years, would I have ever encountered an error due to the package no longer being hosted by Canonical?
Assume problems such as security vulnerabilities or system instability were never found in that package/version.