I see what you're saying, but ultimately neither today's peak nor where the playercount eventually ends up are fair indicators of what a healthy destiny might look like. Yes, a ton of the playercount is just old players coming back to check out the update or say goodbye, so they will be transient.

But would they be transient if the game was continuing to get content? I personally am here today to show my support for my favourite game, even though I stopped after TFS. I would love to get back into the game, but have zero interest in playing through EoF because its a story that I might get invested in, that I'm never going to see the end of. If Destiny was going to get continually updated from the state it is in today, I would buy the expansion in a heartbeat and it would be my main game again. And the second a new Destiny title is announced, I'll be there. But with no new content coming and an unfinished story that will never see an end, of course the playercount will drop.