I have no idea how it came loose, but it happened while driving. I made it home about 3 miles away but I am afraid that the crank shaft seal is now destroyed becuase it is leaking some oil. What should I be afraid of?

The fan and all, or just the pulley? If the fan and pulley came loose, and it is held

on with multiple bolts, Damn I hope it isn't the crank. Drop the engine and look.

I have to look to see if the fan came loose.

What type of engine? If type 4 then the pulley is part of the fan and the fan is attached to the crank with 3 bolts. If you mean that the pulley came off of your alternator then that is not too big a deal. Did you just lose the belt?

I did not lose the belt. The crank shaft pulley is the pully that came loose, not the alternator pully. I will be looking at it later today and I will take pics and show you.

Did the fan come off the crank hub (2)? Or did t he crank hub come off the crank?

happened to me once, it was the single crankshaft bolt holding on the flange which receives the three bolts for the fan. Replaced it with no ill effects. I did have to drop the engine to find all of that out.

You can get to it by pulling the fan housing.
Not a real big deal. Pretty easy actually.

Inspect the crankshaft's morse taper and key way very closely before putting it all back together.

The odds are NOT on your side that damage to this critical interferance fit has been avoided. If the taper or key is damaged the hub will never stay tight again, no matter what is done.

If the taper and key seating areas are damaged a complete tear down and crank replacement is necessary. I have seen them compromised from driving 500 yards.