I have seen it stated several times on these forums that the Constitution does not grant any rights, it just protects the unalienable rights already possessed by individuals. That would mean that these folks had those same rights.
However, by becoming terrorists and being captured, they have forfeited those rights but would have whatever rights are enumerated in the Geneva Convention, to which the US subscribes, concerning prisoners of war.
I am not familiar with the GC, but would think holding the prisoners until the end of the war would be permitted.
I would guess this is a different war than addressed by the GC, and maybe it doesn't qualify as a war under the it, but I would take it's provisions as the "default" rights of prisoners.