How have “seasoned” nurses transitioned into retirement? I have worked in a level 3 NICU for 27 years and love my job. I am thinking of going part-time(2 shifts a week). I am currently on intermittent FMLA taking care of an ill husband. Advice?

There is nothing more important than your relationships. Taking care of your husband is a priority. If you can afford to go part time, do it. You didn’t say how old you and your husband are. You may consider meeting with a financial planner to see if you can afford to retire.
I am a retired nurse practitioner. There is a transition to retirement. But, there is actually so many things you can do. Do you and your husband have any dreams you have been putting off? Now is the time to do them. Do you have any hobbies you wish you had more time to do? Do you have grandchildren?
There are also many volunteer opportunities. I could list them forever.
Once you have settled into retirement, you won’t miss work.
You will be creating new memories in the next chapter of your life.
Good luck. Best wishes. God bless you and your husband.