It's fact that by profession a witcher should work alone. It's a fact that Geralt, for the major part of his adventures through the saga, had some companions with him. Those companions sometimes fought alongisde him, but mainly worked just as friends, whom didn't want to leave the poor man alone to prevent him from commiting something crazy or suicidal (like going all the way down to Nilfagrd to regain Ciri).
I think that, if the companions were done this way, it would work. They'd be independent, they wouldn't follow you around the map to fight(combat areas) unless it would make logic in the means of plot. Instead, they'd be always somewhere near in the "hub" area of each Chapter. They could stay at your camp for example (if the gameplay would look at some point like a long journey through forests/mountains) or at the Inns by the road where you stop for the night. I'd also like them to have way more dialogue options that they had in TW2 (triss, zoltan, dandelion, roche, iorveth) that would reflect the current actions and their in-game consequence.
I think something along this path would reflect Saga tomes 3-5 most accurately.
P.S: Sorry for typos and mistakes