Depends - is the future set in stone, H2G2-style (the Stavromueller Beta subplot, specifically)? If I cannot change the future by my actions that means I will

Depends - is the future set in stone, H2G2-style (the Stavromueller Beta subplot, specifically)? If I cannot change the future by my actions that means I will be completely safe from dying until the appointed time is near, so...