4.3 broke some things, and I think I'd rather wait for the fixes before re-deploying 4.3.
sheepishly answering my own question. Per http://docs.splunk.com/Documentation/Splunk/latest/Installation/Upgradeto4.3onUNIX
Splunk does not provide a means of downgrading to previous versions; if you need to revert to an older Splunk release, just reinstall it.
Regrettably, that is a failing on Splunk..... there is no going back.
sheepishly answering my own question. Per http://docs.splunk.com/Documentation/Splunk/latest/Installation/Upgradeto4.3onUNIX
Splunk does not provide a means of downgrading to previous versions; if you need to revert to an older Splunk release, just reinstall it.
Tell us what broke, perhaps we can help.