Trading all of they guys like JD, Osuna, Sanchez etc (unless you get ML talent in return) isn't a retool. It's a rebuild. That's not necessarily bad, but I think it's clear that management has no desire to do that.
I could understand Happ getting moved (he'd probably net a good prospect in return), and he's older. Liriano and Estrada, given that they're free agents at the end of the year, would be good targets to get some salary relief on. I doubt we'd get anything useful for them, but keeping Biagini in the rotation would have some value for us longer term. Bolsinger would probably produce similar results as well (albeit with much less upside), so it likely wouldn't hurt our competitiveness this year much.
We could always go for something less conventional too. Verlander is likely available for example. While his contract the next two years hurts (a lot), maybe you can find some kind of fit there, especially if the Tigers are willing to package him with someone in another area of need in exchange for taking the whole salary and maybe some lesser prospects. JD Martinez, for an unlikely example, would look really nice in LF for the remainder of the season. Someone like Joe Jimenez would look real nice in the pen too.