Unfortunately David, I think those sides are cactus. Bending a cutaway in figured wood is quite a big ask of the wood in the first place. Reversing a cutaway in figured wood is next to impossible whilst leaving the sides in good condition.
I've bent a lot of cutaways in figured blackwood - a couple
here and
here. A few things for next time: 1) Thin the cutaway side to 1.8mm "north" of the waist and keep that constant right up to the end of the side 2) Don't profile the sides before bending. If you get cracks beginning to form, they nearly always start from the edges. If you profile the sides after bending, you have a good chance of cutting out any cracks. 3) Only dampen the inside of the curve when bending. You'll have a lower propensity for fibre starts on the outside of the curve if you keep that side pretty dry. 4) Set the temperature of the bending iron so that you don't get scorching. You'll need to allow more time for the heat to penetrate the wood, but you'll save that time in not having to sand out burn marks. Wood bends a lot more easily than charcoal.
You may be able to rescue parts of your "old" sides for bindings or for laminated linings or even for figured wood purfling. Remember that all the linings, bindings and purfling have to go around the cutaway, too. So have a think about what species of wood to choose for the bindings, if you don't rescue some of the blackwood. You can't thin the bindings in the cutaway area. A final use of the blackwood if all else fails is to use it for headstock facings.
On other subjects, I'd recommend going with the truss rod. I put truss rods in all my classicals, which improves playability significantly. As it's a cross-over, you'll likely be playing with a lower action anyway, so a truss rod will be a big help with the set up rather than having to guess any pre-relief based on no data.
Also (as I think you've already discovered) the sequence of operations for the rosette inlay is to join the top, level the joint, inlay the rosette, level the rosette, then reduce to final thickness by removing wood from the underside of the soundboard. Then cut to outline and finally cut the sound hole.
Good luck!