in this case im pretty sure it won't poof suddenly, it will stay until it naturally dies.Not sure I would suggest a private server to anyone in any game to be honest, they can disappear any day without barely any warning even if they are active as hell. Kinda makes the time spent on it feel a bit of a waste also forcing you to start all over again in a new server (official or not).(I actually say this out of my own past experience in games)
but even if that risk was actually present.. it would still be better for new players, with how heavily p2w and grindy the official servers are.. a new player has to either spend their life savings or grind for 8 hours daily like it's a job. both of which are not worth so i won't recommend it for anyone.
so yeah, even if p-serves didn't exist.. i would tell a friend to stay away from it.
Although everything being easy and have r8+10 / 99+15 all sp cards in half a month is also a bit uh... I think a middle road would be more ideal.
I do agree though that there should be non-mall options for scrolls and upgrade stuff.
If let's say Nosmall or Nosmallers disappear for a month nobody will be able to upgrade anything which is a bit uh...