Near the end of my install of SP1 I got the error message in the subject. Upon copying the error:
TITLE: SQL Server Setup failure.
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SQL Server Setup has encountered the following error:
The NT service 'MSSQLFDLauncher$MSSQL_2012' could not be started.
Error code 0x84B20001.
For help, click: http://go.microsoft.com/fwlink?LinkID=20476&ProdName=Microsoft%20SQL%20Server&EvtSrc=setup.rll&EvtID=50000&EvtType=0xAE7B8BF3%25400xF762992B%25401202%25401
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BUTTONS:
OK
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And hitting OK, setup just disappeared. No further indication of whether it was going to rollback or recommend a repair, etc.
Further investigation into why the setup failed show that SP1 appears to have actually installed the FullText Filter Daemon on this particular instance of SQL 2012 all on it's own. We had not installed that to my recollection, as we didn't have any intention of using it on this server. To further back that up, we use domain accounts for all of our services relating to SQL Server, and the FullText Filter Daemon was set up to run under the default account as if we had just installed it and not set any account, and since that default account didn't actually exist on this system, the service failed to start during SP1 installation.
I switched the service account to run FTFD under to LocalService, and then that service started correctly - but the SQL Server service will still NOT start. I'm currently doing a repair, and I'll post back on how that pans out.
Regardless, there appears to be scenarios with the SP1 installer where it will have a rather catastrophic failure, and there's a good chance it has to do with not having the full text filter daemon installed.