They will get quite scratched up with use, but they'll work just fine. As long as you're getting consistent cuts with them you don't need to replace them
It is good practise to keep an extra set around because, Murphy's law being what it is, the day you have a ton of cutting to do, that'll be the day one either breaks or stops working for you!
just my opinion - used similar Sizzix products for scrapbooking for years, and years and didn't replace them.