The main reason for US/NATO not to renounce first strike was because it would be fairly easily overwhelmed by Warsaw Pact forces if WP attacked conventionally. Probably some kind of large WP exercise turned real very quickly combined with Spetsnaz causing havoc behind NATO lines.

First strike was needed in order to slow things down and do some damage, in theory to a) give the US time to rush conventional forces to Europe, b) bloody the nose of WP enough to make them think twice and c) destroy as much as possible of the WP rear areas and reinforcements. If the WP had gone through the Fulda Gap or the South option near Switzerland -tactical nuclear mines, Special Operations nuclear devices, tactical nuclear artillery, tactical aircraft attacks etc would have been used pretty quickly on them.

In reality it probably would have escalated to far worse than that pretty quickly I'm guessing.