Declaring migration bankruptcy

I joined a project recently that has 2 years worth of migrations. It
is about to go into production and I am wondering if we should
consider clearing out most of the history. A poor decision made early
on has caused the project to have about 20 custom plugins (all of
which really belong in the application). One task involved in moving
the code out of plugins involves all the migrations. The way the
plugins are set up, there is a migration in the root application which
calls the plugins migration. So there are two files for every plugin
migration. We could certainly take the time to merge them all but I
wonder if it is worthwhile. There is no way we are going to migrate
back several months at this point (let alone years) so I question the
value of old migrations.

So, my question is what is the downside of deleting old migrations
(let’s define “old” as more than 3 months old on an active project)?