Jep,
When you declare MAYDAY that call is a broadcast to any station listening that you have an emergency situation. The MAYDAY call is strictly to get everyones attention that you have a very serious problem requiring immediate assistance.
In my 17 years I have never heard someone broadcast that I'm cancelling my MAYDAY. In your example if your engine restarts and appears to be running normally you can tell the ATC facility that responded, that you are cancelling your emergency, and that the situation is under control or remedied, you may cancel your emergency but state that you want to still make a precautionary landing at another airfield.
Either way ATC may ask that you contact them upon arrival at your destination to ensure that you landed safely.
Mike
NATCA FWA