I know that Addictive Drums, Melodyne and Rapture will port over as they are 3rd party full versions (or in the case of Rapture a separate Cakewalk product that may go away when Sonar does.)
 
What about the AAS, Blue Tubes, TH2/3 (non upgraded versions), Sonitus, B Reverb, True Pianos, Studio Instruments and Session Drummer (I might have missed a few)?

Tried these in Studio One 3 - 
Adaptive Limiter - N
Bluetubes - N
Bifilter - Y
Breverb - N
LP EQ - Y
LP MB - Y
TH2 - N
Studio Instruments - Y
Addictive Drums - Y
Session Drummer - Y

I'd very much like to know if DimPro and Rapture (the versions that come with the Splat download) will work in another DAW. I use these synths in nearly every one of my projects. I don't know if they're completely separate VSTs or if they're somehow tied to Sonar. And do they require online re-authorization (like Sonar does) in the event of moving to a new HD or some sort of Windows update issue?

I'm not sure about online re-authorization, but I've just tried Dim Pro and Rapture in Studio One and both work absolutely fine - all the presets show up as well.

I would like another company like Steinberg, Native Instruments whoever to save Cakewalk Rapture Pro and keep it going.  I bought Rapture Pro back in the summer of 2015 and I love it.
 
I own SONAR Professional and even though I'm bummed out to see it go, I own other DAWS (like Steinberg Cubase Elements 9) so I can continue my projects by moving MIDI files (most of my projects are MIDI based).  But I'd really like to have Rapture Pro still available.  I want another company to pick it up like what happened to Alchemy when it was acquired by Apple (even though it sucked for Windows PC users like myself since it became Mac-only).

Thanks, Red Dwarf. I assume you just set Studio One to scan the folders containing the Rapture and DimPro .dll files?

red_dwarf
I'm not sure about online re-authorization, but I've just tried Dim Pro and Rapture in Studio One and both work absolutely fine - all the presets show up as well.

Both work in other software. Most cakewalk owned products do except some pro channel modules and adaptive limiter

Yes, in Studio One, from the start screen - Setup -> Locations -> VST Plug-ins. I've got C:\Program Files\Cakewalk\Vstplugins listed among others. You can enable/disable the startup scan on this panel, as S1 takes well over a minute to scan my plugins.

What won't work are the DX based plugins like Sonitus. That's a shame but I'm sticking with Sonar till it dies or I do. Even if I have to load up a computer with windows 7 to do it.
 

The only plugs that shouldn't work are those tied to Sonar with special licensing like BREVERB, TH2 & 3. The Sonitus plugs work in Reaper. Don't know about SO3 or others yet. Unlike Sonar, most of the demos I've tried so far automatically scan for plugs without any input from the user.
 
Oddly even Sonar has plugs that only work in certain versions. IE: VGA+ only works in Home Studio 7, the last home studio before the latest one.