Not as bad as it could have been.

The front of the engine, the flywheel is off and the gear case has been opened up. All the bolts came out without problems and the cover is undamaged.
The water pump drive is the gear on the top right which is a bit rusty but it is only surface discolouration and will clean off, the other gears, the chain and the inside of the gear case are free of corrosion which bodes well for the inside of the engine.
So it's a new water pump, replacement bearings in the gear casing and then 3 oil changes, two filter changes and a full service.
Should be done by end of the week provided the spares are all in stock as promised.

Moral of the story?
Keep and eye on your water pump weep holes!