Well maybe there can be the best of both worlds here. Whilst the devs I'm sure would love to see this succeed even if there was no money in it, something needs to be done to ensure it's financial continuity. So you could do something that not many have done before.
First though, if the devs decide to go with F2P they can NEVER have P2P. So many people who join after release would be OUTRAGED by it and think either; The game is sinking and becoming money grubbing. OR Plain and simple "I wasn't paying for this before, why should I start now?" So you would safely assume that P2P to start with would be a safer option to provide an ongoing income for the game.
Now yes that also raises complications about not as many people playing because of the monthly fee and then if you charged say $50 to buy the game as well that might turn even more people off.
But.....
What if, on release you charge that $50 (I would happily pay console game price if this game turns out like I think it will) but instead of charging $10-$15 monthly sub.... you instead charge a $5-$10 sub, with a discount to buying the game in early access stage. Say, $24.99 a pop.
That way, you gain a large community before the game is launched. You get to stress test everything while getting some funding as well. You launch with the $5-$10 P2P option and charge $49.90 for the game itself. Now when you look at those numbers compared to a lot of other games being released these days those prices will jump out at you.
"Oh sweet this game is UNDER $50"
"Holy hell! $7.50 for a month! Just means I eat at home tonight instead of getting McDonalds."
Both of those will just leap out at people and you will still have the best of both worlds. A P2P system at the start to provide some semblance of financial security and a low sub price to keep people there and bring more in.
That's just my opinion anyway. Feel free to point out pros and cons