If Santander is healthy he for sure should be in the lineup. As good as Lukes, Schneider, Straw and Clement have been those guys have weaknesses that good teams/pitchers can expose. Those guys are valuable over the course of the season but in the cases of Schneider and Lukes they really struggle with high velo fastballs up in the zone. They feast on mistakes/bad pitching which there isn't much of in the postseason.
I'm also not convinced Santander ever gets healthy this year. Sounds like a serious Labrum injury and that surgery is inevitable if he isn't even swinging a bat now.