Can't be done, and one of the reason why KD left since the Max has been grant to Klay instead of him.
Ans speaking with their ages it might be no longer on their prime if in case that particular deal happened(which probably far from reality)
There is no way Steph goes to Lakers, there is no way that they could handle both Lebrons contract and on top of that Steps contract and AD's contract all together somehow. But aside from the financial part of the deal I can easily say that Steph is doing awesome in GSW, what could be the reason he would leave?
I mean if he was a player that never won a ring with GSW and was playing amazing like this year, he may leave and go chase a ring with Lebron but Curry already has 3 rings, from now on he could just get paid a lot of money and have fun, that's all that matters for him, he could lose and still just have fun and that wouldn't matter. Plus they are getting Klay back next year, I am sure with everyone healthy they are going to be able to do something decent, after all they were without Durant first time they won the ring and they will be great again.
Those desperate to have a ring are easy to move and find stronger allies, but that's not the case for Steph he already proven everything and he created he's statue with the rest of his teammates,.