DROP LOGIN fails on SQL Server 2014
For SQL Authentication logins, this is no different in SQL Server 2014 than in previous versions. I just did this in 2008:

CREATE LOGIN dbowner WITH PASSWORD = 'x', CHECK_POLICY = OFF;
GO
CREATE DATABASE mydb;
GO
ALTER AUTHORIZATION ON DATABASE::mydb TO dbowner;
GO
DROP LOGIN dbowner;
GO



  Msg 15174, Level 16, State 1
  Login 'dbowner' owns one or more database(s). Change the owner of the database(s) before dropping the login.


I can't drop the database until I do this:

ALTER AUTHORIZATION ON DATABASE::mydb TO sa;


For Windows Authentication logins, As Dan pointed out, prior to SQL Server 2014, this check wasn't performed for Windows logins, so you could leave databases in a weird state by dropping their owner. Your second option sounds best to me, and it only means adding the above line to your script. Another option is to just not make a Windows login the owner (I'm not sure why you're making them owners instead of just giving them appropriate rights in the database), or stop dropping the logins as part of the process, or both.