If your postulate is true, can souls in Gehenna-Purgatory be bought (or otherwise earned) out of their suffering?
Hey God, let's make a deal!
Bought?
No.
But the prayers of the living can help the living souls in Gehenna just as the prayers of the living can help the living. (See 2 Maccabbees...I will give you chapter and verse later).
God is the God of the living Abraham and Isaac. Bodies may be dead, but they're still alive nonetheless. This is Jesus in Matthew. Once again, you have to wait for the cite until I have time.
Getting myself fired right now in order to have that discussion would be a sort of earthly Gehenna to which my wife would add some scourges and maybe an asp, so I am going to go radio silent, but I have not run away and I have not forgotten you. Please keep a list.
Oh, and no, you're not going to go to Hell forever or maybe even at all for getting the doctrines wrong and fighting about it. Don't blaspheme the Holy Spirit, and you'll eventually get to heaven: Jesus said so.
And follow the mitzvot of the Torah, as modified by Jesus (kashrut is no longer required, see Mark), and don't do evil, and love God with all your heart and your soul and your mind and your strength, and you will probably be able to skip the Gehenna part completely and go straight to Gan Eden.
As for me, well, I'm afraid I was a young man once, and I still have a young man's mind, so God will have to be really, really forgiving to let me off the hook without some purgation. The Church says it's all forgiven by confession...but if you go right back to your vomit (in your mind, anyway), well, I'm not looking forward to my life review. I deserve some pretty nasty things, all told.