OK Pete, my condolences on your loss, but I'm sure you are used to it by now. I'll just mind my own business.
There are some tricks of the trade for getting screws out without damaging the slots. Once you damage the slot, you are down to a list of unsatisfactory options. The secret as long as the slot is undamaged, is to make the downward force on the screw much larger than the turning force to undo it, and that is difficult in your situation. The easiest trick is to use a hammer-operated impact driver to undo the screw, but if you don't have one, that option doesn't exist. There is an even better device but you'd have to make one, and that probably isn't practical. It consists of a Y-shaped top welded to the shaft of the right sized screwdriver, to make a Mercedes star. All you then do is lay a piece of solid bar into the top Y, at an angle in the direction you want the screw to move, and tap the bar into the base of the Y. I don't recall ever seeing a situation where that didn't shift the screw. Caution: if you use this trick for tightening screws, you will always overtighten them until they shear off. Unfortunately you have to make one of these star-screwdrivers for every size and shape; replaceable bits introduce a little bit of slack, and the tool becomes completely ineffective (I've tried it).
