The fine art of being a diplomat, or: whom do you kick out?

This is the dilemma:
1) You invite somebody to dinner. You do it 10 days in advance, but just on the phone, and the person says they're free.
2) Said person isn't really notorious for their infallible memory
3) You receive written information re. that person being out of the country till the day after the planned dinner
4) You hence change the guest list
5) You receive oral but 100% reliable information that the person is actually back in the country.

What do you do?

a) Bank on the person's bad memory, leave things as they are and hope they won't remember when they see you tonight
b) Tell the person, "I'm sorry but the invitation is cancelled, since I changed the guest list based on the information re. your absence till the 7th"
c) Ask the person whether they're still available, because you really need to know

If somebody applied a) to me -- I have an excellent memory and *would* remember the phone call -- I'd feel more than a little offended, and I'm not as paranoid as The Person. Therefore a) is a bad idea.
b) wouldn't be such a bad idea if The Person wasn't Mr H (for reasons I can't really go into, but suffice it to say that deep shit might be coming his way soon, and I don't want to create the impression that I'm taking sides because I'm not)

So I did c). By email, written in Arial 12, which he ought to be able to read even if he forgot his glasses. So no excuses. And if he doesn't respond, his problem. If he does and is still free, I'll have to kick out a friend (the one who's married to the guy working for him and shouldn't be sitting at the same table).

Let's see how it goes...