Sometimes (on the request of the local community), the CMs mass replace some dead links by new ones. See, for example, this post (and Shog9's answer): How to find and/or change a set of hyperlinks on a site?
The tool is a simple search-and-replace tool - it can replace a given string in the URLs by another string. This is typically used when some frequently linked domain changed the structure - but it can still be fixed in an automated way.
Question: Does the tool used for bulk replacement also check whether the new link works?
I suppose that it shouldn't be too difficult to automate the check whether the link returns a 404 error. Basically the question is whether this check should be done by users of the site (before requesting the mass replacement), or whether this is checked by the Stack Exchange software when the links are being replaced.