If my understanding of cryptocurrency wallet programming is correct, then the following is true:

*Any given wallet of any given coin, when met with multiple block chains from multiple nodes, will pick one block chain.

*This preference for a particular block chain is usually based upon whichever chain is the biggest (difficulty * blocks, or described as having the most number of blocks with the greatest difficulty)

*If that is correct then a wallet on a bad chain will automatically rebuild itself if it finds a block chain that has a higher result when multiplying the difficulty of the blocks times the number of blocks

*Assuming that is all correct, all we have to do is connect to those bad nodes with our good wallets and those other wallets will fix themselves over time (though it will be a big download for them)