Greetings,
Mr. K. Strange. There's no wiring on that side of the engine that could have been knocked loose and even IF wiring was knocked loose, if a diesel engine turns over, it usually starts. Your mechanic basically did exactly the same thing all of us Lehman owners do every oil change (take out plug, drain, replace plug, refill with 1 pint) so it should fire right up.
How good is this mechanic? Might he have damaged the Simms pump in some way?