Tindall would be a smaller loss? He's likely fourth choice at best when everyone's fit, assuming Roberts or someone else doesn't jump ahead of him. He played in 13 games this year and may be looking at a lot less next, as he got some games ahead of Briscoe, who was out for a fair while.
Johnson would be a loss, but he needs to take his chances when he gets them. I'd be a bit surprised if he left, as he's one of our few other halfback options and two hookers isn't enough in a squad.
Just on Olpherts, Fusitu'a played less than half the games this year and Newman hardly at all. Smith may want Olpherts as an experienced player who may have to play a lot of games. The alternative would be to go with Tindall or someone even less experienced, or to sign a good quality player who might only play half a season. The latter was probably the assumed route if Hardaker stayed, with him and Olpherts being the experienced backup. I assume signing a centre was always the plan, and the offer to Hardaker reflected that while he's a good player he would have been second choice behind Myler, Newman and the new centre if everyone was fit.