As I understand it the reason Jim Jones resorted to a death pact was because he faced extended jail time for fraud. Otherwise he probably would have been happy to continue as a cult leader indefinitely and it never would have happened.
The GB would similarly need to be in a corner and facing existential crisis for this to even arise as a possibility. As it is at then moment they have a comfortable lifestyle with few problems. This is nowhere near on the horizon.
Even if some of the GB were to face prosecution and a lifetime in jail for some reason at some point, because of the developed structure of JWs it is likely there would be others in the organisation who would take over control and replace them. So even if the JW leadership faced a serious crisis, their developed structure also militates against them successfully taking down the membership with them in any death pact.
So I don't think this is at all likely or worth discussing much. In some ways it reflects a sort of ex-JW fantasy because it would deliver final and conclusive proof that the JW leadership are morally bankrupt. But we don't need the GB to initiate a death pact in order to prove they are morally deficient. Their everyday decisions and actions to date already prove that for most clear thinking people looking at the evidence.