What happens when a bad package is in Debian stable?

[Peter Michaux <petermichaux@gmail.com>]

Hi,

Suppose there a nice package has been in Debian stable for years. If a
new version is added to Debian stable and problems are discovered
after it is added, what happens to fix the problem?

If the new version can be fixed? Is a fixed version added with a higher number?

What if the new version cannot be fixed? Is the new version of the
package simply removed? Is an even newer version added that actually
matches the previous working version until bad one can be fixed and
added again?

Thanks.

Peter