No point in splitting up the herd, it is a veterinary issue at best. Besides, if you wish to contain the virus you much first isolate its source. Transfer or transport out would be the worst possible option or way forward.
What Whipsnade's curatorial and vet management need to determine is the source of the infection, which individuals in the herd have been exposed to EEHV, which ones are carriers and which ones are non-carriers and determine which individual may have been the potential source of the EEHV virus (not that this in itself would have any repercussions on this particular individual) infection.
Efforts need to be intensified to find an effective treatment for EEHV in Elephas maximus, both adults and infants (the latter category being the more vulnerable). If I am correct, several herds in continental Europe do have surviving calves and adults from previous EEHV infection. We need to take the research from there.
Efforts for treatment of the human herpes simplex virus and simian herpes virus haven't been very successful to date. While learning from previous disease progression and treatments in surviving calves and adults can be useful, there may be something else at play such as a previously unknown strain or mutation in the virus and I'm sure it is being investigated.
I am fully aware of the med./vet. implications of both viral diseases. And the very nature of a virus is one which is mutative (and sometimes very much so). Still, it puts the onus on finding that effective treatment (viz Tamiflu with new strains of flu, yet being someway effective). ZSL has its own research programme on EEHV (several other major EU institutions likewise).
So, specifically, is the opinion on here that ZSL should:
(A) Retain the same animals and prevent breeding until it is known for sure which ones are carriers
(B) Carry on their breeding programme and research for better treatments in the meantime
(C) Disband the herd to non-breeding situations and start again with new founder stock
(d) another option or combination of the above
I think your options underestimate the prevalance of this virus within the elephant population.
It is currently thought that this virus is far more common among both captive and wild elephants (african and asian) than previously recognised and that the only reason the mortality rate is so high in captive elephant calves is that they and their mothers are not exposed to enough serotypes of the virus so they have a naive immune response.
This would mean there is an argument to continue breeding these herds and in fact increase the exposure of these animals to the virus to afford better immunity.
Andy