If it's mycoplasma, no, not for good. That bacteria is really hard to kill. We studied others of its type in vet school; the darn thing is actually shaped like a corkscrew and literally burrows its way through flesh and tissue and lies dormant until the bird gets stressed or the immune system is otherwise weakened and then there's a flare up and you have to treat again. If they just have respiratory infections, yep, they'll be right as rain in no time.
A lot of times respiratory infections happen when the birds are cooped up for prolonged periods in a coop that has too little ventilation, which happens a lot in the winter when the birds don't want to go out.