Earlier this morning we got a notice from a dedicated reader that Stern will be leaving Terrestrial as of today. The fuel for the rumor was almost validated with this flyonthewall entry:

Viacom B-Howard Stern to leave VIA.B early VIA.B is severing ties with shock jock Howard Stern four months before his contract ends and allowed him to go on air this morning to say goodbye to listeners. David Lee Roth is rumored to be replacing him on the air. :theflyonthewall.com

But listening to this morning's Stern show you knew quite obviously that it was a big joke. If you've listened to Stern for any amount of time you could clearly smell the prank a mile a away.
Billboard Radio Monitor has more on this.