Unfortunately, it is not possible to simply ignore or set aside a strike.
Vimeo is legally required to maintain and implement a policy for dealing with accounts of repeat infringers. Part of this policy includes assigning a strike for all unopposed claims of copyright infringement.
Whether or not the videos are currently available is beside the point when it comes to the Repeat Infringer Policy. If there is an unresolved claim of copyright infringement against your account, we need to assign a corresponding strike so that we can remain in compliance with the DMCA.