Unless the slots were transferred in advance to another corporate entity which also holds an AOC and Operating Licence, they cannot be sold now that Monarch is in administration. Lots of precedent for this being the case and if an auditor of the ilk of KPMG believes otherwise, then they are being badly advised. There was certainly no sign of a transfer to another entity.
The Boeing deal has shades of the support for Laker from McDD and the engine manufacturers almost three decades ago. I can't imagine other Boeing customers would be too happy about it.
On that subject, most airlines like easyJet and TUI are openly referring to the reasons for adding extra capacity and talking openly about Monarch. Is it just me, or do Jet2 seem unable to even utter the M-word in any of their multitude of press releases about expansion and extra seats? Their inability to mention it could almost signal a small element of contrition on their part there, were it not for the fact that it is such a ridiculous notion given the characters involved.