I've had my comic running consistently for almost three years now, never had a buffer, and I haven't had to take a hiatus yet (knock on IKEA particle-board). If God forbid I got in a situation where I had to abandon TLT for an extended period of time, I'd definitely be open and honest about my absence, and try to put something up in the comic's stead, such as scanned rough sketches, historical documents or fan art.
Some people will just abandon their comic for months on end without giving any indication or reason for the absence. At first you think, okay, no big deal, we'll probably get a new strip in a matter of days. Then after a few weeks, you begin to wonder if they permanently abandoned their comic. Then a couple months pass without so much as even a "I'm swamped with critical issues that must take priority over my comic, so I don't know when or if I'll be able to update again" note. And now you're wondering if the person's even still alive. While I can sympathize and understand about having to take care of personal or family emergencies, at least let your audience know what's up, you can be as vague as you want about the cause. I just don't want people losing readers - regular ones or potential new ones - over a comic being AWOL.