With the new iOS 6.1.3 beta already being tested, planetbeing just posted yesterday that the update already plugs one the evasi0n exploits which in turn will obviously mean that if you wish to keep your untethered jailbreak....well just don't update and stay put. Quote from planetbeing below:
"If one of the vulnerabilities doesn’t work, evasi0n doesn’t work. . . We could replace that part with a different vulnerability, but [Apple] will probably fix most if not all of the bugs we’ve used when 6.1.3 comes out."