What should I do if my mother-in-law Liang can't go back for her 50th birthday because of work?

Be sure to give a big gift, so that you can have face when you have relatives. You can make a phone call or send a video. Now video is very convenient. This kind of filial piety is not necessarily worse than yourself. What the old man reads is this heart, and what he cares about is the face of outsiders. You did it. She has nothing to be unhappy about.