I'm not sure, but I don't think you can transplant a Powertab freehub to a Shimano wheel.
If you can't figure out any other workable options, you don't have anything to lose by trying to patch up your original rim as best you can. Unlace the wheel or at least slacken the spokes, brute force the rim as round and true as you can get it, then relace and true. You probably won't be able to get it perfect, but you could possibly make it rideable until you can make a more proper fix.
As for what that fix would be, I think the most straightforward option with off-the-shelf parts may be to replace the rim and lace it to your existing hub. What kind of rim do you have? Is it a common one, or maybe you can find one with the same ERD that would allow reuse of your original spokes? (Thereby eliminating the need to source spokes of the right length or have them cut to size.)