I think if they release it as OSS some people would eventually fork it and maintain it.
Except it doesnt work, don't forget that endpoints ( *.google.com or other google subdomains) are hardcoded in the printer firmware out there.
Over time, if the cost of creating a new thing for a company is maintaining it forever, a lot less new things will get made.
I'm frustrated at the fact that this comment, and many others elsewhere on this, are creating the false dichotomy that Google either needs to ruthlessly kill products that many users are still using (Reader, Cloud Print, ...) or alternately support Every Single Product Forever.
They can still kill their outright failures, of which there are many.
Isn't this the kind of project that should be reserved for people in explicit learning states such as (for example) novice hires, new hires, and aspiring mangers who haven't done any management before? It doesn't really have burning deadlines, it's not a frontline project but it's still something that can be referenced as work with impact, there's still the technical challenge of keeping it functional as the years go by, and eventually it will actually be old enough to be taken out back and deprecated. If any company could do something like this with their various projects as well as culture, I'm pretty sure Google could.
Of course there are probably a bunch of problems with this idea, but it seems to be more preferable in contrast to just axing a product that a not-insignificant number of people found useful and going "NEED. NEW. SHINY. TOY. MUST MAKE MONEY NOW!"