new totalobj[TOTALNUMBER_OF_OBJECTS];

public OnGameModeInit()
{
      totalobj[0] = CreateObject();
      totalobj[1] = CreateObject();
      totalobj[2] = CreateObject();
      // rest if the objects

      SetTimer("RespawnAllObj", 60000, 1); // here it keeps on repeating the respawn process on every 60 seconds you can increase the time if you want.
}

forward RespawnAllObj();
public RespawnAllObj() // main function which the timer does. After every 60 seconds this process is repeated.

      for(new i = 0; i < sizeof(totalobj); i ++) // this is a loop which take all the objects from totalobj and destroys.
      {
          DestroyObject(totalobj[i]);
      }
      //Then recreate them, just use the code you used in OnGameModeInit to create them:
      totalobj[0] = CreateObject();
      totalobj[1] = CreateObject();
      totalobj[2] = CreateObject();
      // ... Rest of the objects.
}