Wow, that is a lot. if there really are 600 that's over $100K a year for Dale, JEEZ.
There are many who have accounts but only play FSO and scenarios, so you won't see them in the melee.
At any one time only a percentage of the melee players are going to be online at one time due to real life and times zones.
Only HT knows. If I were placing a bet, I'd say between 500-1000 total active accounts. SWAG..600'ish.
Taxes, bandwidth costs, he might still have investors he has to split revenue with...etc.
And the population is declining not growing as far as I can tell. If by mortality rates for the average age of the remaining players if nothing else. Not many online games have a constant stream of obituary threads. That should tell you something about the demographics.
You might occasionally recycle a previous player until they get bored again. You might get a few refugees as the remaining sorta competitors collapse. I see no realistic possibility of the current game design\graphics\monetization model having a renewed population growth of new players.
I'm amazed he has kept it going this long. However, the remaining players are here because of social bonds and not feature sensitive. The price seems to be sustainable to who is already here, even if not attractive to new players.
It will probably be milk-able for a while. However given the age demographics and lack of new blood, at some point all those old farts will start dropping all at once as they all hit their expiration date simultaneously. It won't be a linear decline. That isn't going to happen tomorrow, but it's inevitable.
But it was certainly an impressive run. A part of MMOG history.