You just don't trade Z unless it is for a clear upgrade.
Right now, who would be a clear upgrade over him?
McJesus
Draisaitl
Bedard
Kucherov
Matthews
Marner
Bennett (?)
Tkachuk 1 and 2
Barkov
Celebrini (possibly)
That's about it.
Now, who of those is even remotely available?
Marner and possibly Brady Tkachuk. Both of which are highly unlikely to end up here and coming with much higher price tags salary-wise. Marner would be a UFA, Tkachuk would cost an arm and a leg in a trade.
Do any of these fit our age group?
Marner will turn 28 at the end of the season, so he fits in somewhat, but is probably 1-2 years too old for a long-term contract with our core group.
Tkachuk just turned 25 and fits our core group, but we would probably have to add heavily in a Zegras <> Tkachuk swap, which makes it, effectively, undesirable.
We could very well throw 12M per season at Marner and hope he actually likes playing off the microscope rather than sitting in the hockey world's hotbed. But would he really change the needle so much for our organization?