I am facing similar situation, I have seven 2.5year old hens. 3 of which are great broody hens ( they are buffs) how long will they continue to be good broodies for? Are they worth keeping after they are done laying? How long do most buffs lay regularly for? Is it worth keeping them through/ after the fall molt? They will be 3 March. Will I get another decent year of laying?
No one can tell if or when any individual hen will go broody. There are just no guarantees. But if those three have been going broody in past years odds are they will go broody again. It's a genetic trait and those three seem to have it.
If you hatch eggs laid by hens that go broody and keep replacements from the offspring, those pullets often have a tendency to go broody. Again no guarantees on individuals but I did that, kept replacement pullets and a male from egg laid by hens that went broody. After a couple of generations I had a flock where practically every hen went broody at least once a year, some a lot more often. Those genetics are passed down by both males and females. That actually became aggravating, I had hens in my broody buster almost all the time.
How long do buffs regularly lay? It depends on the individual a lot more than the breed. I don't know what breed your buffs are (there are a lot of different breeds that can come in buff) but I'll guess they are all the same breed. How often do buffs of that breed go broody? According to you it depends on the individual, three do and four don't. Laying is the same. Some individuals of the same breed will lay well later in life, some will not.
Commercial laying flocks consisting of the commercial hybrid layers will lay really well their first season and their second. But after the next adult molt their productivity declines by about 15%. At that point that's enough of a drop that the commercial operations don't consider them worth feeding through a molt to get that kind of production. That is not an individual average, that is a flock average. Some individuals will continue to produce gangbusters, some will practically shut down. You can't tell which will do what so they go by flock averages.
Your buffs are not commercial laying hybrids. Who knows what your flock average will be? A lot depends on the person selecting which chickens get to breed. If that person selects to hatch eggs from hens that lay well later in life in a few generations you have a flock that tends to lay well later in life. If that is not one of their selection criteria then it's more just luck. If yours came from a hatchery it's highly unlikely (practically assured) that laying later in life is not a criteria. If they came from a breeder it is possible but certainly not assured.
I can't tell you what any of your hens will do next season after a molt. Seven is not a lot when it comes to averages anyway. I'd expect the ones that usually go broody to go broody again. I'd expect some of them to lay pretty well, some not so well.
With what I think your goals are I like Mosey's idea, replace the ones that don't go broody and keep the ones that do. Renew the flock yet retain the chance of broodies another year. Whether you buy new replacements or keep your own is up to you.