Reminds me of my first car back in 1978 when I was 17 yrs old. An old Toyota with a hemi engine. The valves needed adjusting every oil change, 3000 miles or sooner. I dropped a non-magnetic nut down an open spark plug hole. The plugs had to come out to get the valve cover off, and so of course I managed to drop something in there.
So I had to pull the cylinder head off. I didn't have more than a cheap set of K-Mart wrenches, so I hopped on my bicycle and rode a few miles to a tool rental shop for a torque wrench. Then over to the dealer for a new head gasket.
The coolant had to be totally drained, but we had a gravel driveway...
When the cylinder head came loose, the remaining coolant hiding in the head dumped out, into the crankcase. Pretty soon most of the engine was laid out on the garage floor in pieces.
My words of wisdom to you would be to drain your oil and try to find that foil. It has probably already been chewed up by the pump and sent into your engine, but maybe you'll get lucky and find it. It may also be trapped in your oil filter already. Aside from that, I wouldn't disassemble anything further.