Hello Julio,
I don't think there is an official/supported way to get these back. But it looks like they are stored in the rc_version table. I just ran a test where I deleted a project and it changed the archived value from false to true. To get it back I needed to run the following sql statement (mysql) for it to reappear in ROC:
update rc_version set archived = '0' where name = 'Project_ABC';
But deleting the project seems to also delete the Deployment Plans (which seem to be stored in the rc_release_candidate table which also have an achived flag).
Kind regards,
Gregg