Post a few pictures of the rotor caps. They can be seen easily by folding down the chopper and climb up the ladder to the back of the rotors. How many hours? They should last well over 1500 hours IMO. Maybe the flights at the very front of the rotor need replaced. Some of those can be done with it still installed in the machine, but it isn't real accessible.
Pulling the rotors is quite easy, if doing both it takes about 8hrs, a skidsteer wont lift high enough. Like seedcleaner said they maybe dont need replacing. Check the elephant ears at the front of the rotors, they are the first thing to wear and can be changed from the grain tank, not an easy job.
If you do remove the rotors make sure to change front bearings, full set of rotor wearing parts will set you back $10,000 plus.
If you pulled the stock impeller out to replace with a sunny brook, it would be easy to replace the elephant ears and check rotor bearings at that time. Picked up a 760tt from rice country, 700 separator hours had worn over an inch off the chromed rice elephant ears. We built them up them ourselves,took new bolts ,rice had burned off the heads. You can get at most from the impeller area. The sunnybrook will let you use the added power of the 780. Good luck! tiger