No, but some shin gaurds if you go riding might help. just kidding, all you need to do is keep a tight grip in case she tries to throw you over the bars.
Sometimes you can reuse the gasket and sometimes not. A fresh gasket less than a year old definitely, an old gasket I don't think so.
If the plunger has fallen out, you'd know it. strange sounds would eminate from below.
oops not those, the ones coming from the engine. And unless someone has really screwed up by say leaving the plastic piece that locks the plunger in the housing, the chain will stay tight on the cogs until all adjustment is gone. And the timing shouldn't float until it come undone. While it's not unheard of a chain failing at your mileage, it's unlikely. If you intend to do it tomorrow, and put it back together and ride the day after or so, I'd go get a gasket.