Bent like a banana crooked, or twisted so the wings wouldn't be level with the tail? I know it's severe in your estimation, but my "severe" may be your "oh, I can barely see that", or visa versa -- can you give us numbers somehow? Like is it twisted 5 degrees from nose to tail, or is the centerline bowed by 1/8", etc.
Is the fuselage floppy where you've cut it for wing access, or did it go "sproing!" and now it takes a lot of force to make it go straight?
There's different in-between answers for each possible problem, but every single one starts with "if the fuselage is rigid but bent, and if the wings, engine and tail all line up correctly it'll fly right but look odd". They all end with "yes, it's hopeless, stomp it and start over again". And note that "hopeless" depends both on your taste, and on how soon you want to get done.
If it's floppy because you've cut out a lot of structure, but you can hold it straight in your hands, then your problem is just one of work-holding while you get the wing in. As soon as you glue it back up again it'll be a rigid assembly again. In this case I'd say figure out the work-holding part (maybe figure out how to get it back into the jig, with shims beneath that top block) and get on with the work.
If it when "sproing" when you cut the last fiber of wood that was holding it straight and it really resists being bent back into shape, then either you forced it into shape in the jig and glued in a lot of stress, or the wood had a lot of internal stress that you relieved when you cut it. Either way, you're either going to need to make more cuts and glue it back together straight, or you're going to have to assemble a straight engine, wings and tail onto a crooked fuselage, or you're going to need to stomp it and start over -- and hope that you don't do exactly the same thing again*.
If the above hasn't made your decision for you, tell us how it's bent and if you can figure out a sensible way, tell us how much. Maybe include a photo if you can figure out the process.
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* Tangentially related story: My dad built custom cars and restored antique cars. Someone brought in a boat-tailed model T roadster that had been originally built back in the early thirties or late twenties. They wanted it restored.
The thing had a persistent warp in the boat tail -- he could chase it around, but he couldn't make it go away. After a lot of frustration he grabbed some flat sheet, cut out pieces exactly where the original builder had cut their pieces, beat out a new boat tail and welded it up. When he was done, it had the same warp.
Which is a really long way of saying that rebuilding a warped-up thing doesn't always save your day.