On the positive side you have gained experience in an reputed firm. Knowledge gained is gained irrespective of your employment status. Now that you senior left, escalate this to your immediate Superior or HOD. Once you moved to regular role please ensure that your off role experience is mingled with Regular role in terms of while getting a experience certificate from them upon separation in future.
7th August 2019 From India, Madras
Immediately approach your Senior colleague who has replaced the Sr.HR and get the regularization done.
Persistence in the pursuits will show you the result, and more over have you been given any offer letter during your off roll employment with a stipulated condition to take on rolls post your probation/training?
If yes go with the terms mentioned in it or else get it through frequent representation through your senior as suggested earlier.
8th August 2019 From India, Hyderabad