My DH and I moved abroad a few years ago for work. DH used to see his mum every few months when we lived back in the UK, and they call each other one a week/message.
My DH has gone back to London this week/end (5 days) for work and arranged to see his DM for dinner. He was really excited to see her and they had planned this a few weeks ago. She lives in the middle of the countryside with her husband (DH stepfather) so it was a bit of a drive, but considering she might not see her son again this year - definitely worth the trip and she does go to the city quite often ( so not impossible).
As soon as he landed, she let him know that she had a headache/sore tummy and would not be coming to the city to meet him for dinner. He is also free this weekend so could see her on another day, and she could not meet on the other days due to some other plans that do not seem important. For context, this is not the first time with the headache/tummy - she gets this issue quite often and I'm skeptical of it.
AIBU to think that if there is a chance you will not see your son for quite some time, you would want to make some effort to see him? He made the effort to fly half way around the world and adores his DM.
My own DM for context would persevere through a medical emergency to make sure she could see me when I came over. I'd do the same for my child too.