Was Kayano's recovery affected by Heaven's Spear?
Heaven's Spear was only fired once, 


  and Koro-Sensei dodged it. 


During that period, the students were not there. It was never fired again.


   After the fight where Kayano was mortally wounded, they killed him after he saved her. The manga basically ends there and there was no more follow-up as it was considered resolved.


The students were never hit with the beam.