Supposedly Hunter is close. But agreed, I'll believe Robertson when I see him and Neshek might be out until August (if he's out as long as Hunter and Robertson).
No way to know how they'll perform because with relievers there's never any consistent approach/result. Even as older players they may come back better, if initially rusty, because rehab and rest is better for their arms then three months of pitching.
(Neshek did not, however; in fact - again, with usual small sample/bullpen caveats - you can argue that he might be done. FIP and WHIP were bad last year for first time since 2015 and it's all bad this year.)
Deadline deals are rarely overpays. Nobody gives up their top guys for relievers or FAs-to-be. A controllable high-leverage guy, maybe.