Big news! We've been big fans of 37signals for a decade or so and in many ways they have inspired us in building Close.io. I love that they are able to make the hard decision to focus on one thing. We want to take great care of any Highrise customers looking for a new home: http://close.io/highrise Check out http://close.io/ - mention that you were a Highrise customer and I can make sure you'll get a special discount…
Your comment implies Highrise is going to disappear - however, that's not the case. They're either going to sell Highrise (to a buyer who is committed to keeping it running + growing) or continue to run it themselves in maintenance mode.
Highrise was an amazing product years ago, but let's face it, Highrise has almost been abandoned for the past couple years at least. Could a new owner take over and revamp it to be amazing? It's possible, but not the common outcome of acquisitions.