They had really intended to have a rotating DH. Schwarber and Nick probably would have gotten 60 starts each in LF. At DH, those two plus Harper some, Bohm some, JT a little, maybe even Didi (except he was done). Of course we didn't even really have a CF that year either (Vierling, Herrera and then finally Marsh).
Schwarber probably could have gone back to LF if he had to. He was really struggling with his knee and his conditioning then though, and not playing the field has made him better, as much as it's also made the OF defense better. He's the flip side of Casty really, they made the same bet on a player who had just as many warts coming off a great year, and Schwarbs delivered.
The funny thing is what DD did that year is kind of what people seem to want this year. The line-up looked pretty set, it could have been better but it's not bad, and then Nick was just still sitting there and DD decided to gild the lily/increase the budget. Bichette certainly more appealing now than Nick was then, if also more expensive for that reason. Bellinger seems pretty much just like Nick and Kyle (age, some up/down seasons) with better defense (though I gather his CF days should really be over).