You can get just about anything you want on the top of the CPU without worry. It's only a heat spreader; just a flat piece of metal that has nothing to do with the operation of the processor except for cooling. Nail polish remover, motor oil, peanut butter, whatever - as long as it comes off, you'll be fine.
I mean, I wouldn't recommend any of that, duh, but as long as it's not something electrically conductive, it's probably not going to cause any permanent damage. What you really want to watch out for is if anything slopped off the sides and went under the heat spreader/onto other components/etc.
Yes, you'll want new thermal paste. You're supposed to re-apply it every time you take off the CPU fan, and operating without any would be super dumb.