Nah you can skip having wyll in your group, plenty of ways to finish without him around. Start at the druid grove early on if you wanna grab him but honestly, the main story keeps rolling either way. Maybe interesting to know his devil stuff with mizora and that whole thing with duke ravengard later adds some flavor, but nothing game-changing. The story adapts real smooth whether hes there or not and other companions like karlach or shadowheart can handle whatever you need done. Tip though if youre into the whole narrative thing his personal story does add some neat context around act 3, but you wont miss any crucial bits without him just some extra dialogue here and there.