The tech description mentions that the old Herc Mk. 1's are now used in security operations or even as targets. I guess it may make a good trainer also.
Summed up some of the old FS1 era fighters using the BP tech description:
GTF Hercules: Target practise (presumably as drones) and security operations (I imagine defending low-profile depots or civilian spacelanes). Retired from the front-lines. No longer produced.
GTF Ulysses: Seems to have served and may still serve as combat evaluation fighters. Retired from the front-lines. Produced still, but in small numbers.
GTF Loki: Most spaceframes were sold off, I assume to mercenaries or civilian contractors. Presumably retired from the front-lines, but not all spaceframes were sold. No longer produced since the NTF rebellion.
GTB Medusa: Described as an obsolete bomber, it's only mentioned in the past tense. Probably no longer used on the front-lines. Presumably no longer produced.
GTB Ursa: Still in use but considered a dead-end design-wise. Still in use on front lines. Perhaps still produced for it's role as heavy bomber, unless only previously produced Ursa's are used.
GTB Zeus: Has been used for a while as Trebuchet delivery system, now is a training target (presumably as drone). Mostly removed from service, very likely no longer serving on the front-lines. Assumably no longer produced.