Like a month ago, folks were talking about moving on from Lindy to give Key the 8-year bag.
Miller is a 2nd pair guy, even if he has some highs and lows. I agree with you on Mikkola, but have to push back on the bolded. Miller is a "#4" already, and there's really no ceiling. He could top out as a Mikey Anderson with added offense, a left handed Trouba (who's hopefully cheaper and a bit more reliable), or an absolute freak of a unicorn. But he's definitely a top 4 D today.
Back to Lindgren though, we need to plan to keep him until his body can't keep up. In a year, f we can follow up this contract with an Anderson-like $4+ until he's 31/32 (just not the same 8 years), then Fox's entire prime will be completely covered with a perfect partner.
You can't get a Chychrun or Gavrikov unless you want to move on from Lindy, Miller, or whichever new guy after next season. Lindy's too important, Key has too much upside, so if neither Jones nor Robertson are in the plans for next year, then we will NEED someone for next season...but no further. We can't afford Chychrun or Gavrikov next year or beyond, so if Mikkola'a not looking for a 1-yr deal for similar money, then it's either a kid or we have to find someone for next season. I'm not giving up 55 or 79.
This season, as long as we don't completely forget how to play hockey when Lindy's out (again), we'll be just fine once he gets back. Creates a little cap flexibility, too. If you want to get freaky, then Mikkola could be a trade chip for even more cap flexibility and you can even try a kid out with Schneider for a couple weeks.