Have I ruined my stylus?

Leaving the stylus running in the lead out groove isn't good in my opinion, when you consider the back and forth shock involved when the cartridge is thrown back into the inner part of the lead out grooves. Will 8 hours ruin your cartridge? I'd inspect it with magnification as suggested by George, maybe play a common record on it and see how she goes. Common sense tells me that this may break down the suspension pre-maturely, and it may weaken the shaft (imagine bending a solid core wire back and forth. Over time the wire developes a stress point which it eventually break at). While inspecting under magnification, I'd look closely at the shaft for stress points. Cleaning the stylus is also a great idea, however I'd inspect the stylus under magnification first, then clean the stylus, then re-inspect. This will give you an idea as to the effectiveness of your stylus cleaning method. I use LP#9, which works very well.

Hopefully all is okay. Keep us informed!

consider it to be your normal stylus wear. if you have a diamond stylus you can scratch the match lightning surface and nothing will happen. it's realy more the cantilever issue to determine the cartridge wear.

i used to have 5 year-old benz glider worked with no problem, never damaged the records and sounded and probably still sounds great with tens of thousand hours on that.

Heck no!
Consider all the hours you have or will have. Consider in all those hours all the clicks or pops you might get. How meny records do you play in a row? Ever listen all day?
Hope this gives you some confidence. I, too, have done this, left my cartridge on all night (meticulas, but not perfect) more than once, with more than one cartridge.
Question- if I play records all day, stopping only to flip them, and clean the stylas, is this more prone to wear, and also, what are the best cleaning methods in addition to those (or that) described above?

STYLAST & the green microfinishing film....