Something to consider.
1.
There are specialists around that shops hire to re-thread professionally something that may have had the threads ripped off. I wonder if it's the frame, or just the threads that have been damaged by an over zealous impact wrench from someone trying to secure it? Some mechanic could cover his ass by saying it's rusted out, as an example.
I've done this myself, where the bolt for the rear sway bar snapped off, and I did a poor job of removing the old one. When drilling out the old one, I screwed the thread up.
I went to my local shop and they contacted a professional to rethread it for $100.
It's held for two years perfectly and shows no sign of stress.
2.
Depends on the condition of the subframe/cradle.
Beware to look for cracks around the control arms brackets.
If this is as rusted out, to rip a bolt out of a sway bar, you need that bottom section inspected very carefully for no structural things about to give way and cause a more serious issue.
A great video here at South Main auto on a rusted out cradle from an Altima.
Eric O channel is great.
1st video shows the damage caused by rust. Looks at the structural cracks! This dude was lucky.
https://www.youtube.com/watch?v=A_G34PM ... oRepairLLC
2nd video of a rust free cradle install.
https://www.youtube.com/watch?v=q8V4oy6 ... oRepairLLC
I'm certain you can find rust free cradles if you need them on Car-Part.com. I would look to down south, in the dry States. I've searched and there a number of hits.