1 The distance between them is not so great as (it is)unbridgeable.-------as /so -- - - as 是结果状语从句
==The distance between them is not so great as TO BE unbridgeable.(表结果的简单句)
== The distance between them is not great to such a degree / extent that it would be unbridgeable (结果状语从句)
2 The punishment was harsh because Maggie would lose her position,but it was not so bad as to lose her pay.
对的,只能用doing,因为要和前面逻辑上的losing her position相对照.或者：
== The punishment was harsh because Maggie would lose her position,but it was not so bad as the possibility of losing her pay （动名词做定语）
=== The punishment was harsh because Maggie would lose her position,but it was not so bad as the possibility that she would lose her pay.（同位语从句）
3 it was not so bad as losing her pay (was )-----括号裏面的was加与不加已经没有什麼意义了.
4 我给你的方法已经是最简单的了.
5 The distance between them is not so great as (it is)unbridgeable.-------就像我早先说的,应该是--------.The distance between them is not so great as TO BE unbridgeable.或者：The distance between them is not so great that it would be unbridgeable.