I am sure that there are much more knowledgeable persons here on this board (Silverbull, Coach, GWR a.o.) on this matter, who may have the exact answer. I would think that management/BOD can decide on the term of warrants like they can decide on the placement of shares (within the limits approved by shareholders).

I think there is a strong case for the extension of the term of the warrants by Golden Minerals, since they were not in the money at the time of the merger and the share price was very negatively affected by the merger, as we all know.