This would be reasonable In my eyes! And Marner might want out and a low profile team with less media bashing and great weather plus a good young core coming together might not seem that bad.
I absolutely hate the idea of trading Mario after trading Hertl. This team needs a leader as they rebuild and you have to be careful about trading all those guys away.
But this is pretty fair. Marner would obviously be flipped at the deadline and possibly get back more that what they're giving up here, while helping Celebrini develop.