I was 55.5 yrs old and met the MR-75 in my surplus in early 2019, I was a "management" level employee in mobility. Back then, MR-75 let you keep the subsidized medical plan, other than that, there really wasn't any value in it.
Severance was 1-week base pay per year in service, up to a max of 26 weeks The payment is approximately 4 weeks after separation, just taxes are withheld, no 401K, insurance, etc.
I forget the last regular paycheck, I believe it was on the regular payroll schedule, may have been a mailed check
re-employment with the company, there are documents at the benefits site. I believe if you rehire less than 6 months after you left, you may be required to repay some portion of the severance pay.
Employment with contractors, that's completely separate, between you and them.
It's all a bit fuzzy now, 4 yrs later, I'm no HR/Benefits, or any other specialist. I know there are differences based on what part of the company you are from, when and where you were initially hired, and whether you are union or management, so what I went thru isn't necessarily the same as anyone else. Certainly, it is different after Dec 31, 2021. Good luck.
You will get your pro-rated bonus. My last day was 3/31/2019, in 2020, I got a bonus check for that quarter, that was the end.
The benefits center, you can make an appt / call with them and they can go over current options and how to pay for them (again, back in 2019 I could easily continue medical/dental/vision/life, etc., or not)
Fidelity is the administrator of the pension and 401K, you can call them and they will advise on what options you have