Converting RTF in a text column to plain text in bulk
I ended up making a CLR function to convert it.

I found this library, I then tweaked it a tiny bit to remove things I did not need like logging and Drawing methods, which allowed me to mark it as safe.

I then just made this small class.

using System.Data.SqlTypes;
using Itenso.Rtf.Converter.Text;
using Itenso.Rtf.Support;

public partial class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlFunction]
    public static SqlString RtfToPlainText(SqlString text)
    {
        if (text.Value.StartsWith(@"{\rtf"))
        {
            RtfTextConverter textConverter = new RtfTextConverter();
            RtfInterpreterTool.Interpret(text.Value, textConverter);
            return textConverter.PlainText;
        }
        else
            return text;
    }
}


And ran this in SQL

sp_configure 'clr enabled', 1
GO
RECONFIGURE
GO

CREATE ASSEMBLY ConversionsSqlExtensionsAssembly 
from 'E:\Code\ConversionsSqlExtensions\bin\Debug\ConversionsSqlExtensions.dll' 
WITH PERMISSION_SET = safe
go

CREATE function RtfToPlainText(@value nvarchar(max))
returns nvarchar(max)
AS EXTERNAL NAME ConversionsSqlExtensionsAssembly.StoredProcedures.RtfToPlainText


And it is fast and works great!