Consider that Trump was already talking about the election being 'rigged'.
They didn't want widespread public awareness of their spying on the campaign, as that would have proven Trump's point.
And the spying had ALREADY taken place - the Dossier was needed to create post-facto legal justification via a FISA warrant in case she lost (plus explain why the FBI investigation existed).
So there were multiple elements to the insurance policy.
But its not clear whether it would have been quietly dropped, or used by HRC to demonstrate Russian interference in her march to war in Syria.
Personally I think the whole thing started in 2015 as part of that agenda, and repurposed to Trump in mid 2016.