を[経「へ」]て => After A N1
Time, Situation
~をたて(~を経て)      => through; after; via N1
[後「あと」]で => After V1, V2 N5
Time
〜がさいご(が最後) => if you do... negative result N1
Decisive (resolute decision)
たが[最後「さいご」] => Once A occurs, B happens N1
Information, Report