A word for someone willing to make sacrifices or drastic decisions [duplicate]

resolute TFD

Firm or determined; unwavering.

unrelenting

1. Having or exhibiting uncompromising determination; unyielding

2. Not diminishing in intensity, pace, or effort

Such a person is committed to a cause or course of action:

[Merriam-Webster]

2 : having made a pledge or commitment to someone (such as a romantic partner) or something (such as a cause)
// committed partners
// a committed parent/teacher
// strongly committed to the fight for equal rights
also : characterized by such a pledge or commitment
// two people in a committed relationship

Also see the referenced pledge:

6 a : a binding promise or agreement to do or forbear
6 b (1) : a promise to join a fraternity, sorority, or secret society
6 b (2) : a person who has so promised

In the case of a binding promise as it relates to a pledge, it means that you will do so something even if it is difficult.