When one reads the post, on the surface, it can be concluded that performance appraisal and separation from the company are two independent things. The former is for measuring employee performance in the past performance cycle, whereas the latter is his basic choice on how long one will serve in a particular company. If the employee finds his interests lie outside the company, then where is the problem? As long as the employee serves the notice period as per the notice period, everything is fine.
Your question is on the legal repercussions of separation after the performance appraisal. However, it should be noted that performance appraisal and resignation are internal matters of the company. Labor laws do not deal with the internal matters of any company.
Nevertheless, if one reads between the lines of your post, one feels a grouse that you might have on the resignation of the employee after the salary hike. Is this the real reason for your post?
Thanks,
Dinesh Divekar