Hi Folks,
Are you planning to upgrade the Junos or only the FPC Firmware?
You should not lose layer 3 function in either way. License should not get affected in general. Proactively you can take a backup of the license to a text file.
show system license keys > /var/tmp/license.txt
and add it later with ‘request system license add’ cli. Use ‘show system license’ to verify the license once added.