Spirit Airlines also does not serve peanuts on the flights that I have been on to Orlando from Detroit.
My son is also one who is extremely allergic to peanuts and he has flown to Holland, Florida, been to WDW and cruised on the
Disney Cruise Line with no reactions.
No, you cannot guarantee that someone will not eat peanuts behind you on the plane but if you fly on an airline that does not serve peanuts you at least have a better chance of avoiding them.
There are peanuts everywhere in our lives. You have to live your life as safely as you can under the circumstances.
If you start to think too closely about it you will want to lock the allergic person up in a bubble. You cannot guarantee that doorknobs, library books, money, telephones, and the list is endless are peanut free.
So you just take as many reasonable precautions as you can and carry on.
My son is now 20 years olds and lives his life as normally as a non allergic person does. He has the mindset that he maybe some day peanuts may get him, but he is going to live his life to the fullest until that day.
With all of the advancements and research going on with this allergy there is hope for a better, safer future for all peanut allergy sufferers.