...save WB a multi zillion dollar search for a new man to wear the cape?
A talent search, even when it's extensive, is chump change in the context of a major blockbuster. Searching for a new actor to play Superman might take time, but it wouldn't be all that expensive by the standards of studio spending. The only way finding a new Superman would be costly would be if they signed an established major star.
If they do a reboot then Routh has to go in my opinion. Keeping him but casting a new Lois and dropping Jason would be too discordant and it would seriously muddy the clean break WB would need in marketing terms for a Superman relaunch.