Tenants disappeared and their friend gave back keys and vacated

[David Dong]

My tenants rent was already 5 days late and we agreed to meet last night at 7pm for me to collect. When I got there nobody was home so called/texted them, both their phones are turned off. I wait a while and supposedly their friend came by to clear out their stuff and gave me back the house keys. She told me that they left on an emergency flight back to the mainland and were not coming back. No idea why, no notices, no nothing. I was just contacting them this morning about me coming down tonight for the rent and the tenant said "sure". I have a pay to quit notice signed by the witness that im going to post up on their door. Am I allowed to change the locks and re-rent? Can they come back and am i legally obligated to keep the unit empty? Desperately in need of some advice as I have never dealt with anything like this. I have their security deposit as their lease was supposed to end in june. The only thing left that the friend couldn't take was the bed that they purchased. 

As of right now, I will be filing for an eviction. My main concerns are. Am I legally allowed to terminate the lease due to abandonment and change the locks before the eviction goes through? I have an abandonment clause in my lease stating that " If the tenant vacates or abandons the property, the landlord shall immediately have the right to terminate this agreement."