I've thought in view of its sustained success in the wild , if its not time for another attempt at captive breeding. My thought is the original failure was due to putting all twenty in the same 280 ha enclosure. On the other hand the protected area that most live in is not all that much larger. Still with the growth, a few taken for captive breeding would be very little risk.
It would be useful to have a second satellite population. A captive component might be a third option.
Article on plans to expand the populations of tamaraw The ambitious plan to recover and rewild the feisty, dwarf cow no mention of captive breeding- which again I believe should be part of the mix