Be sure to consult with an employment lawyer who is knowledgeable about ERISA, before you sign a general release and waiver (in order to receive severance); you may have an ERISA section 510 claim if you are let go when you are close to meeting the rule of 75. That means significantly reduced pension benefits if you leave before meeting the rule of 75. The termination may constitute a denial of ERISA benefits and age discrimination.
Also, class action lawsuits are possible for this type of ERISA claim.
Don't leave voluntarily and consult with an employment lawyer before signing away your rights!