たが[最後「さいご」] => Once A occurs, B happens N1
Information, Report
~んがため(に)/~んがための      => in order to ~ N1
めったにない => Rarely N3
Degree. Level, Amount
めったに~ない => hardly; rarely; seldom N3
〜がさいご(が最後) => if you do... negative result N1
Decisive (resolute decision)
ため => In order to, for N4
Purpose, target
ため(に) => For, because… N4
Cause and Effect
[後「あと」]で => After V1, V2 N5
Time
めったな => hardly; rarely; seldom N2
Ban
たろう => probably is ~ N3
Speculation
あらためる => to revise; to replace N3
Happens next
…たら…だろう => If only... N3
Condition (condition contrary to reality)