Pronoun ambiguity is a slightly grey area on GMAT - what's considered acceptable or not seems, in some cases, a little arbitrary. That's why I'd encourage you to look for issues in some order of priority. A comparison issue definitely trumps pronoun ambiguity. Actually, I'd say that you should analyze pronoun ambiguity only as something of a last resort.
In any case, I don't think this is a particularly borderline example. What counts is that the meaning is clear. Since there's no way that 'severance packages' can have a 'last scheduled day' we're not going to get mixed up with the meaning of 'they' or 'their'.