Probably not, if it catches in the window assembly it’ll just rip it up. It may clog the drains in the door once it falls to the bottom, but you can just clean those out, shouldn’t really be an issue.

Well what car is it? If you’re lucky it may have automatically shut itself down when it saw it didn’t have oil pressure, saving itself. If it doesn’t have this function, then the engine probably siezed and is done for.

Yes it’s a nylon washer, totally legit. I have one on my vehicle right now, it is not leaking. I’ve found they can actually be tougher than metal crush washers, require a little bit more force. When tightening I like to tighten, loosen, tighten, loosen, tighten, the drain bolt to really crush and seat that washer, same with brake crush washers.