All of that is true

Well, we know he was killed in the German air attack. Presumably he was killed by a bomb, but I suppose it's possible he was strafed just the way Carol was in the car.
Yes, it might be nice to know where, how and under what circumstances he was killed, but ultimately the filmmakers simply didn't think it was important. Besides, it would have required either showing what happened to him (which would have meant either not showing Carol getting killed, which was obviously more important, or showing both of them getting killed, which would have been, well, overkill); or else a lot of expository dialogue near the end (which would have spoiled the dramatic impact of hearing the vicar announce his and the others' deaths in church).
Dramatically, his death did seem a little predictable and, rather sadly, trite.

I get that we don't
have
to know what happened to make the point, but I would have liked to know.

Obviously, he didn't make it, or else his shelter wasn't as bombproof as he thought. For purposes of the film's conclusion, it wasn't really necessary to know the details.