Seems like on a 15/yr mortgage wells would just have to return 5% or so a year (dividends plus share appreciation) for him to be better off not touching his 401k?
You also haven't given a lot of relevant info eg
1. How old is your friend decisions are different for a 20 year old vs 60year old.
2. Is the 20,420 account value or it what he will get after taxes and penalties?
This is not advice its just an example of how I would think of this situation.
Withdrawing 20,420 now will eliminate 22,000 in interest over how many years? say 10 years left on the mortgage(just a guess).
Will the 20,420 in WFC stock with dividends reinvested for those 10 years be more than 42,420?