[That depends](http://meta.security.stackexchange.com/a/1839/92273).

Supposed that the ransomware is doing a "good" job, all files will be encrypted with something like AES-GCM, which is (at the time of writing) not (known to be) vulnerable to a [known plaintext attack](https://en.wikipedia.org/wiki/Known-plaintext_attack).

In that case the files might not aid much, only to verify the correctness of a brute forced key.

Also, if the ransomware is doing a "good" job, the key will differ on a per-machine basis, so brute-forcing the key will not help much to retrieve other data encrypted on another machine by the same ransomware.