Not to say Porzingis isn't "needed", of course he is, but I sort of view him as a luxury. Lets be real, we pretty much won the Finals with him only playing 6 games out of the 19 total in the playoffs, and 3 of them were him as a role player.
I'd be fine letting him just not play the first month or two of the season to let him heal, and bring him back from the 2nd half of the season and beyond. We can survive with Horford and 2 of Queta/Tillman/Kornet in the meantime. In a way, it could also give the latter group a bit of experience which they'll gain from more minutes and opportunities which bodes well for the postseason.