I realized something when reviewing Full Metal Alchemist's finale for the umpteenth time. I haven't been giving Hohenheim enough credit.
spoilers:end of spoilers
Hohenheim secures his victory conditions three episodes before the final episode. I've always really loved Hohenheim's plan in Episode 61. Father intends to use the mystical effects of the sun's corona combined with a manually dug alchemy circle during a solar eclipse to activate his transmutation circle when the gates to the heavens open up so he can essentially absorb FMA's version of God as well as the souls of tens of millions of people of Amestris so he will have the power to trap and wield said entity. Hohenheim uses the moon's shadow in that very same eclipse to create his own equally-sized alchemy circle and partially negate Father's spell, forcing the return of the stolen souls to the people of Amestris. Without those souls, Father cannot continue to contain FMA God and is on the clock from then onwards. Father then desperately makes his way to the surface trying to consume as many souls as possible to salvage his plan.
I didn't give enough Hohenheim credit for in this situation because:
(a) He was still significantly below Father's power level and would have died pretty quickly if not for the other protagonists of the story progressing through Father's conspiracy wildly beyond any reasonable expectations.
(b) Father would then have been free to recover enough souls to complete his plan anyway.
But now I realize two other things:
(a) Hohenheim had a deathwish for 99% of the series. He did set out on his journey with the objective of being able to grow old and die with his family, but after Trisha died and his boys grew up he didn't really care if he survived his plan;
(b) It is exceedingly unlikely Father would have been able to secure enough souls quickly enough to salvage his plan. He had spent an incredible amount of time arranging events such that he could absorb about 50 million souls (according to Roy Mustang) at once over an incredibly large nation area. Without this circle, he could only hope to absorb souls one at a time in person while going on a rampage. People are not helpless and Father would have encountered considerable resistance from the now-aware military - most of them weren't in on the conspiracy and even those that were didn't sign up to get soul sucked (tricked with promises of immortality). Said resistance would force Father to use his philosopher's stone powers, further depleting reserves used to keep FMA God in check that much longer. After escaping to the surface, Father takes maybe 20 minutes of real-world time to die. Even with perhaps a less concerted resistance effort as one might reasonably expect without the heroics of people like the Elric brothers, Briggs soldiers and Roy Mustang's faction, Father was not going to make up 50 million souls before running out of juice. More people might have died before Father went down, but Father was almost-certainly going down.
Hohenheim planned his counter around facts that would inevitably occur during Father's own plan. He spent years laying the meticulous groundwork for said counter-plan to work. By the time Hohenheim confronted Father and got his ass kicked in a toe to toe fight, he had already beaten Father, Father just didn't know it yet. Hohenheim really had a thought-through, big-brain plan.
Holy ****!
I haven't seen you in over ten years since you had to do your military service.
How have you been?