I'd challenge the premise of the question. Capitalism is more environmentally sustainable than the alternative, socialism. Under capitalism, the land is owned by people, and thus those people have an incentive to take care of it and protect it for themselves and for their children. Under socialism, all the land is owned by the government, and so people have little incentive to take care of and protect any land. If they trash it, they can just move on to someplace else. In practice, which is better maintained: a rich man's estate, or "project" housing? The government may at any given moment be controlled by people who want to protect the land, but they'll have a hard time carrying that out when the people actually living on the land don't care. And at the next election the rich and powerful may get their people in office who will then give them license to ravage the government-owned lands, take whatever they can get, and move on. Also, in practice, corporations routinely have long-term plans that can extend for decades, while governments rarely plan beyond the next election.
But all that said: Sure, if the people who own the land expect to live for a very long time, whether that's by improved medicine, brain transplants, or whatever, it stands to reason that they would take a longer-term view of things. Today a person who owns property has an incentive to take care of it for his own lifetime, and because he usually hopes to leave it to his children and he wants them to enjoy it. Of course some property owners have no children, or are selfish and don't care about their children. For these people, if they themselves will get the benefit rather than their children, that might give them more incentive to think long term.