You should be able to determine the state of the CV joint through careful visible inspection and simple testing;
- Prior to doing anything, was everything associated with the CV joints working ok (no noises or grinding or clicking or anything else)?
- After removing the old boot, is the CV joint still thoroughly and completely encased in grease?
- Is the grease clean and not contaminated with sand/dirt and not dried out?
- Does the CV joint operate smoothly and easily without any grinding or flat or rough spots?
- Does the CV joint move without any play or slop in the joint?
- Does the CV joint operate without any audible clicks or creaks or other weird noises?
If yes to all of these, then you can probably get by with repacking the CV joints with new grease and replacing the old boots. Of course, replacing the CV joints is always good insurance for the future as long as you're in there.
If the answer to any of these is no, then the best bet is to replace the CV joints.