I got all the witch's heads for the old man in the Companions but when I came back the Silver Hnad had attacked the hall and he was killed. Was he the only way to get the cure or is there another? I just need to know if I'll be a werewolf the whole game now.

Well the quest continues in a tomb, where you give the head to the old mans spirit. There you can choose to get rid of the disease.

Continue with the quest line and you will get the option.

Just an FYI.. after you cure yourself of being a Werewolf you cannot become a Vampire afterwards.

Cool, thanks. I'll just continue the Companions quest line until it comes up