drop off the radar

(idiomatic) To vanish or fall into obscurity.

Example: 2003, Daniel Bukszpan, Ronnie James Dio, The Encyclopedia of Heavy Metal
  Not long after that, the band seemed to drop off the radar entirely, leading many to assume that they had broken up...
2006, Laurie Pasiuk, Vault Guide to the Top Internet Industry Employers
  So why have users stuck with the site when so many other search engines have dropped off the radar? Well, they're not logging on just for the search engine.
5 December 2009, Toronto Star - One-hit wonders make a musical smash
  Greenbaum didn't dramatically drop off the radar as soon as that song peaked, but kept slogging away for five years with diminishing returns...