How many? You move forward until you find the correct one. That's how it's always been. A good guru can tell if a person is "right" for him or her or not. Some have been known to say, "That's not a question for me. You should be with (that teacher), not me," and to in a positive way to send the person onward. (For that matter, many of the great gurus of India attended the satsang of many teachers before finding the "final" one, and Buddha himself deliberately sought out every great master of his era in his quest to find the full Truth. Does Squirts say these persons were wrong to do so?)
Swartz, of course, only wants people to have "one teacher," and for that one to be him. Teach your students its not properly spiritual to change teachers, and they're more likely to stick around, right?
Yes, this is true, the person can move from teacher to teacher and there is scripture that suggests that this is beneficial. I've heard it from the horse's mouth that 'its not usual for the student to change teachers'. This was speaking to a former Shiningworld member who left, and then went back. The opposite is true in traditional Vedanta though.
The reason why a person will have a teacher can also vary. Generally a person is in sadhana (Sanskrit for a 'means to and end'). There's a clear goal. In the case of freedom, or as some say, enlightenment, that is the goal (sahaja). So, the person is in moksha sadhana, a process that is a means to an end for freedom.
Once freedom is attained, the perception that is enlightenment, what then? A person is free to drop everything, and walk away. In fact, in the tradition the student should already be on their own mostly in nididhyasana, the advanced stage of sadhana.
The Jnani (lets say enlightened being) no longer has enlightenment as a goal of course, so can no longer be in moksha sadhana. Yet even though they're free to walk away and abandon Vedanta, often they won't. And this is because they've developed a love for it. So while there's no sadhana for enlightenment there will continue to be study. As there will always be things to learn. It's this accepting that even though the person may be enlightened, may even be a teacher, that they're a student always first, and always learning. It's a humble perspective.
Within the sannyass tradition there are Chaitanya sannyass, and they will retain use of the mantra OM and also a Guru. It's the sannyass that have 'ananda' in their name that have neither the use of the mantra OM, nor a Guru. However, in our lineage even the direct disciples of the head of our lineage, will still regard him as their Guru. In fact, those SWami/Swamini will always keep the student perception in regard to my paramaguru (guru of my guru).
So yea, a person may or may not retain a Guru, and it can be for a number of reasons. Be they Swami/Swamini, or Grihasta (householders).
RV showed his playground attitude and knowledge of Vedanta by trying to make a thing out of a Swami & I parting ways. Such things happen, In the tradition that is Vedanta, it's understood that when two people come together, like in any other relationship that there can be mis-understandings.
We even begin teaching by reciting what is called Shanti Pada, peace prayer. And in that prayer we are recognising that issues can come forth, personalities can come forth, and to not let that get in the way of the knowledge that is Vedanta. Sometimes though, it does happen, and it's simply shrug of the shoulders and a... 'so what'.... If it's a run-of-the-mill difference of opinion, that's the Vedanta view.
I'm not sure what hyperbole RV was trying to troll, perhaps that too was a work in progress..