glad you posted the letter before he sent it:

per flyertalk tos, remove the name of the specific person in your first post (but keep it in the letter).

the letter needs some editing. as other flyertalkers have stated, it's too full of emotion, which makes it less likely to be taken seriously, imho. he should focus on the inconvenience he suffered and ask for a specific compensation that would remedy his not getting it, like a free systemwide.

frankly, the fact that he's been a general member flying (for free on government tickets) probably holds little or no weight with united. the fact that he's planning more international travel in the upcoming months is germane, however.

he needs to briefly detail what happened and how he wants it fixed. let us know what happens.