If you have a backup of the license file, you can get the HWFP of the old server from there (search for "fingerprint" in the lf.licx file). From there you can deactivate from the command line anywhere where you have the ActivationTool.exe program, which should be installed in the Server program files folder. Use the instructions here to deactivate via command line:

https://support.laserfiche.com/kb/1012301

You may also need to have the HostID (MAC address) of the network interface Laserfiche was using. If you don't have either of these pieces of information due to the crash, you will need to open a support case to see if Laserfiche can help.