Should you come across the missing files, let me know at once, please .(happen). If you come across my old wooden box somewhere in the cellar, don't throw it away

1.Should you come across the missing files , let me know at once , please .(happen)
=>...
2.If you come across my old wooden box somewhere in the cellar , don't throw it away .
=>should...
3.The best way to make theme work hard is to promise them a reward .
=>Promise..
4.If a fire breaks out, the emergency exit should be used . (the event)
=>...
5.Were Mike not so affluent a man , Ann wouldn't be dating him.
=>but
6.If you let him go unpunished , he will certainly do that again.
=>Let
7.If you scream again , i'll make you leave the room .
=>Scream ...