I personally wouldn’t bother informaing MB as if they say no then you could be in a pickle.
If you have not regualry abused the system and as such are not on the fraud radar so to speak then you have zero chance of anything happening or even being asked why you used the vehicle on this date etc etc.
Even if you did get asked you could easily argue as others have said that you and your husband were attending together until the last minute when he had to pull due to health concerns and you still attended as his representative etc.
I work with a lady who uses her mothers mobility car to go to and from work, running about and going on holidays oh and taking her disabled mother to the shops once a week.