Yes. The stock portfolio is only a fraction of BRK. They own an entire railroad (BNSF), a very large electricity utility, GEICO and other insurance firms, and dozens of other entities - many would be Fortune 500 firms on their own.
Can aluminum take up the slack? I know long distance power cables are often aluminum. Even some of the larger gauge in-home wires. If copper prices rise too much, some demand will switch over to other conductors.