I'd propose something slightly different. We start a
spreadsheet/wiki/git doc/whatever with a list of all the services and
specific maintainers. Each service must have at least one maintainer.
For those services that don't have a maintainer, they are deprecated.

That's the only requirement...there must be at least one specific
person who has volunteered to maintain the service, which includes all
t-h-t, puppet, packaging, and CI (if applicable). If the service is
not maintained then it's deprecated and will then be removed.

That way, there is a very straightforward path to avoid service
deprecation...maintain it.

Also, folks who generally maintain CI and packaging and keep things
running smoothly for the rest of us don't have to worry about
individual services that may or may not be maintained. If a service is
causing issues and it's documented as being maintained (but it's
actually not), then anyone can propose its deprecation as a way to
come to consensus on its actual state.