Preds have no reason to trade away two players who are cheaper, have more controllable years, than one controllable year of Hronek.
Mikeheyev is about a 1.5m player and his MNTC. Can't think of a reason why San Jose is a desirable destination .

Hronek has higher upside and rights to sign for essentially two rental players with attached draft pick.

Any team willing to take Mikeheyv for draft pick and retention for a salary dump. Doesn't need to be San Jose.

With the departure of McDonagh it really puts a strain on NSH's defense. NSH has several LD's who could step up, but without resigning Carrier, NSH doesn't have a complete RD core (Only Schenn and Fabbro left). I'd be open to moving some pieces around to make room for someone like Hronek to play in that top pair RD spot. I'd prefer someone like Zadorov who can play more physically, but I won't say no to Hronek.

It’s very unlikely for a first time GM to trade one of his first signings after only a year. Nyquist will be a Pred to start the season, although he could be moved at the deadline depending on where NSH is in the standings.

NSH would be better off looking at UFAs like Pesce and Zadorov before doing this trade. Like @AEcho said, they're unlikely to subtract another defenseman with McDonagh gone, and their top six isn't good enough as is. While it's unlikely Nyquist repeats this season's performance, NSH would still be hard pressed to find an equal replacement at that cap hit.

An offensive defenseman like Hronek isn't NSH's biggest need anyway, when they already have a better one in Josi, and his successor on the way in Molendyk. A McDonagh replacement would be a bigger help.