Depending on the timeline for Chabot's return, we could rent another D and possibly flip them at the deadline. Of course, it comes with risks of the D getting hurt.
As far as the original proposal goes, Anaheim isn't going to burn a retention spot and increase their spending/cap for anything but a huge return. They should be able to get a 3rd for Lybushkin at the deadline without having to retain, and maybe a 2nd if they offer cap considerations. There will be very few RHD, and his style will be coveted for the playoffs.
People will bring up the Zadorov trade, but the reason he went for a 3rd is because Vancouver could take him without cap considerations. If Calgary was willing to retain or take back money, they would have gotten a greater return. As we saw last year, prices go up at the TDL when teams are more confident in knowing they are either a buyer or a seller, which opens up the market for third party teams to facilitate trades, and teams to use their banked cap space.
They would probably prefer a 3rd straight up instead of a 3rd+Brannstrom.