alt Hacker News> But the gain can be rolled into another property with a 1031 exchange, deferring taxes. I already said this in the comment you responded to.
They can also keep the property forever and continue renting it out, and then never realize the gain. But in both cases that means they don't get to realize the gain -- or even recover their original principal -- except insofar as they're renting it out, and the rent is taxable income.
Or option 3: get a line of credit against the property and spend it to realize the gain with no taxes. Stepped up cost basis upon death for your heirs.