My situation is as follows: I am a Ukrainian citizen and have a one-year Italian residence permit for the purpose of studying that is valid until June 16. I am supposed to leave the Schengen zone on June 19. My passport allows me to stay 90/180 days in Schengen. I wanted to ask:

 1. Can I stay in Schengen after my permit expires, having the Ukrainian passport, without the need to leave the Schengen zone and reenter? 
 2. In the following scenario: My permit is valid until June 16, but I leave Italy for Croatia (which is part of the EU but is not part of the Schengen Zone) on June 1 and then, re-enter on the very same day with my passport only without showing my permit anymore. Would my student status change to tourit status in this situation?

Thank you for your help!