Well the Nets can offer them more than anyone else, so if nothing else hopefully a sign and trade, but I think all 3 are here because they want to be and if they win a title that curses a lot of problems.
This whole "Nets are built for 2 years and then it's over" is extremely over blown.
They don't have any long-term terrible contracts (other than DeAndre Jordan for 2 years after this).
Do they have a young star under a long-term contract? No.
But just because someone is signed for 5-6 years doesn't mean they aren't demanding a trade soon anyway.
2022-2023 contracts:
Harden (Player Option), Durant (Player Option), Irving (Player Option)
Harris, Jordan, Shamet, Johnson
Worst case all 3 of them Opt-Out and leave.
Nets have an immense amount of cap space to potentially sign players.
If all 3 opt-in then the Nets can potentially extend them and will still have a great core for a number of years.
Good players are always available on minimum salaries and buy outs for championship contenders - see the current roster that everyone claimed was terrible and turns out it's not.
https://hoopshype.com/salaries/brooklyn_nets/