Can we recover Process Model once its deleted?

I don't believe publishing is a factor to this concern.

If the process model were contained in an application that was previously exported from the environment, you could attempt to restore the process model by importing that application.  You may have some object versioning issues to contend with if there are other objects in the package that have been extended since the export.

Robert Shankin said:

exported from the environment

I am trying to build an application and that application is not exported.  

If you're using an Appian Cloud instance, you could contact support and ask them to roll back your environment to the previous snapshot (which i believe are taken nightly).  Note that you would lose all changes made within that environment since the last snapshot.

If you're using an Appian Cloud instance, you could contact support and ask them to roll back your environment to the previous snapshot (which i believe are taken nightly).  Note that you would lose all changes made within that environment since the last snapshot.