well yes and NO
all depends how deep the rust got on it
BUT rather than re blue it if you feel the need
why not have it coated with something better??
like Dura kote, or cerakote, Black ice or the likes(special gun coatings)
its not much more and it will make the gun a 100X's less likely to ever rust again
Plus you can have it coated any color you want then, from flat/matte black to any color you can dream up?
870's are great shotguns , and never a shortage of parts out there
Not saying you have to sink money into it
but something to think about
they have both do it yourself kits and or can send to a good smith to get the finish on!
food for thought!