There is a market for "life support" level maintenance of companies if they get large enough. Look at companies like CA buying (and gutting) companies who have lost their mojo. I think there is an opportunity for people to do this with smaller tech companies.
I think you'd need a certain scale of market size to make it worthwhile. And if you didn't have the size to support continued development, will you have size to support continued maintenance?
On the other hand, if the devs have just moved on, there may be a sustainable company. See https://railslts.com/
