Remember, you do not have to accept a new position at a vendor to Allstate, even if offered to you. It is your decision who your employer is, not anyone else’s.
You accepted employment at Allstate, not company XYZ. If Allstate terminates you — even to go to company XYZ where Allstate says that it has arranged a job for you — you are entitled to say “no, thank you” and take your severance instead.
The “substantially the same position” language does not apply if the company with the “substantially the same position” is not Allstate.
Bottom line: if you VOLUNTARILY agree to accept a job from company XYZ because Allstate asked you to, you lose your Allstate severance and are then covered by company XYZ’s severance policy, which is likely less generous.
Know your rights.