A「あすの朝(あさ)でも発(た)てるか?」
B「必要(ひつよう)とあれば(行(い)くしかない)ね」
A: “Are you leaving tomorrow morning?”
B: “If it is necessary (I will have no choice, but to go).”
the following clause can be omitted. The necessity of doing something is generally implied in that case.