My old 00 sport finally succumbed to frame rust 2 owners later at about 270k miles. The rockers were pretty much nonexistent since about 225k. I sold it at about 210k but then it sat in a dirt driveway as a winter beater for 2 years and never got washed. It went right where the rear control arm attached to the frame. The whole bracket rotted right off. When I looked at it (it then belonged to a coworker) I said we could easily fab a new mount and weld 8-10 inches in either direction and it would be fine. He finally decided to just sell it for parts. It still looked great and ran great (besides the rockers) but it just wasn't worth fixing. He now has a 4th gen.
I work in automotive restoration in New England. We fix stuff like this all the time during frame-off's. Actually have one now that needs a few spots fixed. But the difference is a 3rd gen 4Runner isn't worth the multiple thousands of dollars to fix properly. If you know how to weld sure you can patch it up. But you'll likely be chasing it the rest of the truck's life.