Junos OS

I was attempting to upgrade the j-web package following an upgrade of EX4300s to 17.3. I was trying to remove the old package first, but ended up deleting the jweb-ex platform package  Can the package be reinstalled, or will it still be present in the backup partition, that I coould then boot to?

If neither of those work and I need to reinstall JUNOS, can I just use request software add <package> where the package is the same 17.3 package I used when upgrading?

Good Day,

You can uninstall an Application package by using the CLI command. After the Application package is uninstalled, the Platform package features will still be available for use.

We recommended that you do not uninstall the Platform package. If you uninstall the Platform package, you must reinstall Junos OS on your switch for the J-Web interface to be restored.

https://www.juniper.net/documentation/en_US/release-independent/junos/topics/task/troubleshooting/ex-series-j-web-application-package-faq.html

Do you have the same version on alternative slice? If so, then you should be able to boot into it and platform package should be there as well.

As a second option you can install the same Junos version again.